Fix 'main' attribute cannot be used in a module that contains top-level code

apple/swift#55127

Add argument parsing using ArgumentParser Swift package

- Create options for GitHub URLs or repo and organization (including validation)
- Setup Async commands including one for retrieving PRs
- Rename main.swift to work around swift ([SR-12683](apple/swift#55127))

Implement PR endpoint with PR state filtering and results limiting

- Add Repo struct that maps to the GitHub repo and can be initialized with various forms of the GitHub URL details
- Add PR endpoint and associated types to create and asynchronously fetch PR data from corresponding GitHub endpoint
- Create types for resulting PR model objects
- Add tests for Repo initialization and fetching PRs using endpoint

Update VS Code project with:

- Fix new environment builds by creating package resolve task that build depends on
- Move GITHUB_TOKEN environment variable to env file used by debug launch task
- TODO: Remove postCreateCommand from devcontainer.json so container can be used by VS Code (and doesn't just call swift --version)
- Swift extension incorrectly expects `cwd` being set in tasks but since it can't be hardcoded or use the `workspaceFolder` variable, set it to an empty string

Address Linux build issues:

- Import new FoundationNetworking library yon Linux
- Implement asynchronous version of `URLSession.dataTask()` on Linux where async `URLSession.data()`

Follow up tasks:

- TODO: Refactor top-level GitHubRepo object and delete associated GitHubStatsCore tests

Add argument parsing using ArgumentParser Swift package
- Create options for GitHub URLs or repo and organization (including validation)
- Setup Async commands including one for retrieving PRs
- Rename main.swift to work around swift ([SR-12683](apple/swift#55127))

Implement PR endpoint with PR state filtering and results limiting
- Add Repo struct that maps to the GitHub repo and can be initialized with various forms of the GitHub URL details
- Add PR endpoint and associated types to create and asynchronously fetch PR data from corresponding GitHub endpoint
- Create types for resulting PR model objects
- Add tests for Repo initialization and fetching PRs using endpoint

Update VS Code project with:
- Fix new environment builds by creating package resolve task that build depends on
- Move GITHUB_TOKEN environment variable to env file used by debug launch task
- TODO: Remove postCreateCommand from devcontainer.json so container can be used by VS Code (and doesn't just call swift --version)
- Swift extension incorrectly expects `cwd` being set in tasks but since it can't be hardcoded or use the `workspaceFolder` variable, set it to an empty string

Address Linux build issues:
- Import new FoundationNetworking library on Linux
- Implement asynchronous version of `URLSession.dataTask()` on Linux where async `URLSession.data()`

Follow up tasks:
- TODO: Refactor top-level GitHubRepo object and delete associated GitHubStatsCore tests

Add argument parsing using ArgumentParser Swift package
- Create options for GitHub URLs or repo and organization (including
    validation)
- Setup Async commands including one for retrieving PRs
- Rename main.swift to work around swift
    ([SR-12683](apple/swift#55127))

Implement PR endpoint with PR state filtering and results limiting
- Add Repo struct that maps to the GitHub repo and can be initialized
    with various forms of the GitHub URL details
- Add PR endpoint and associated types to create and asynchronously
    fetch PR data from corresponding GitHub endpoint
- Create types for resulting PR model objects
- Add tests for Repo initialization and fetching PRs using endpoint

Update VS Code project with:
- Fix new environment builds by creating package resolve task that build
    depends on
- Move GITHUB_TOKEN environment variable to env file used by debug
    launch task
- Remove postCreateCommand from devcontainer.json so container can be
    used by VS Code (and not just call swift CLI)
- Swift extension incorrectly expects `cwd` being set in tasks but since
    it can't be hardcoded or use the `workspaceFolder` variable, set it
    to an empty string

Address Linux build issues:
- Import new FoundationNetworking library on Linux
- Implement asynchronous version of `URLSession.dataTask()` on Linux
    where async `URLSession.data()`

Follow up tasks:
- TODO: Refactor top-level GitHubRepo object and delete associated
    GitHubStatsCore tests

Add argument parsing using ArgumentParser Swift package
- Create options for GitHub URLs or repo and organization (including
    validation)
- Setup Async commands including one for retrieving PRs
- Rename main.swift to work around swift
    ([SR-12683](apple/swift#55127))

Implement PR endpoint with PR state filtering and results limiting
- Add Repo struct that maps to the GitHub repo and can be initialized
    with various forms of the GitHub URL details
- Add PR endpoint and associated types to create and asynchronously
    fetch PR data from corresponding GitHub endpoint
- Create types for resulting PR model objects
- Add tests for Repo initialization and fetching PRs using endpoint

Update VS Code project with:
- Fix new environment builds by creating package resolve task that build
    depends on
- Move GITHUB_TOKEN environment variable to env file used by debug
    launch task
- Remove postCreateCommand from devcontainer.json so container can be
    used by VS Code (and not just call swift CLI)
- Swift extension incorrectly expects `cwd` being set in tasks but since
    it can't be hardcoded or use the `workspaceFolder` variable, set it
    to an empty string

Address Linux build issues:
- Import new FoundationNetworking library on Linux
- Implement asynchronous version of `URLSession.dataTask()` on Linux
    where async `URLSession.data()`

Follow up tasks:
- TODO: Refactor top-level GitHubRepo object and delete associated
    GitHubStatsCore tests

Add argument parsing using ArgumentParser Swift package
- Create options for GitHub URLs or repo and organization (including
    validation)
- Setup Async commands including one for retrieving PRs
- Rename main.swift to work around swift
    ([SR-12683](apple/swift#55127))

Implement PR endpoint with PR state filtering and results limiting
- Add Repo struct that maps to the GitHub repo and can be initialized
    with various forms of the GitHub URL details
- Add PR endpoint and associated types to create and asynchronously
    fetch PR data from corresponding GitHub endpoint
- Create types for resulting PR model objects
- Add tests for Repo initialization and fetching PRs using endpoint

Update VS Code project with:
- Fix new environment builds by creating package resolve task that build
    depends on
- Move GITHUB_TOKEN environment variable to env file used by debug
    launch task
- Remove postCreateCommand from devcontainer.json so container can be
    used by VS Code (and not just call swift CLI)
- Swift extension incorrectly expects `cwd` being set in tasks but since
    it can't be hardcoded or use the `workspaceFolder` variable, set it
    to an empty string

Address Linux build issues:
- Import new FoundationNetworking library on Linux
- Implement asynchronous version of `URLSession.dataTask()` on Linux
    where async `URLSession.data()`

Follow up tasks:
- TODO: Refactor top-level GitHubRepo object and delete associated
    GitHubStatsCore tests

When working on the next features, we ran into a [known bug in Swift](apple/swift#55127) that prevents the annotation `@main` from being usable from within a file named `main.swift`.

According to a [note in the docs of `ArgumentParser`](https://apple.github.io/swift-argument-parser/documentation/argumentparser/gettingstarted/) (and apparently not documented anywhere else), this shouldn't work at all:

> The Swift compiler uses either the type marked with @main or a main.swift file as the entry point for an executable program. You can use either one, but not both [...]

So it's a bit of a mystery why it works in the current version...

To fix the problem we rename `main.swift` to `CLI.swift`.

Also, the executable is renamed to `concordium-example-client` to ensure that it never is mistaken for a production ready tool.

Finally, some variables were renamed for consistency and the readme got an overhaul.

When working on the next features, we ran into a [known bug in Swift](apple/swift#55127) that prevents the annotation `@main` from being usable from within a file named `main.swift`.

According to a [note in the docs of `ArgumentParser`](https://apple.github.io/swift-argument-parser/documentation/argumentparser/gettingstarted/) (and apparently not documented anywhere else), this shouldn't work at all:

> The Swift compiler uses either the type marked with @main or a main.swift file as the entry point for an executable program. You can use either one, but not both [...]

So it's a bit of a mystery why it works in the current version...

To fix the problem we rename `main.swift` to `CLI.swift`.

Also, the executable is renamed to `concordium-example-client` to ensure that it never is mistaken for a production ready tool.

Finally, some variables were renamed for consistency and the readme got an overhaul.

# Example CLI renaming

When working on the next features, we ran into a [known bug in Swift](apple/swift#55127) that prevents the annotation `@main` from being usable from within a file named `main.swift`.

According to a [note in the docs of `ArgumentParser`](https://apple.github.io/swift-argument-parser/documentation/argumentparser/gettingstarted/) (and apparently not documented anywhere else), this shouldn't work at all:

> The Swift compiler uses either the type marked with @main or a main.swift file as the entry point for an executable program. You can use either one, but not both [...]

So it's a bit of a mystery why it works in the current version, but not once more features are added...

To fix the problem we rename `main.swift` to `commands.swift`. It also turns out that by upgrading to `swift-tools-version: 5.9`, we can abbreviate the setup to omit the "executable product" declaration and the intermediary directory inside `Sources`.

Also, the executable is renamed to `concordium-example-client` to ensure that it never is mistaken for a production ready tool.

Finally, some variables are renamed for consistency and the readme got an overhaul.

# Vaious cleanup

- Some types and variables that aren't named according to the official [API Design Guidelines](https://www.swift.org/documentation/api-design-guidelines/) but were missed in #21 have been renamed appropriately.
- New type aliases for identity parameters are added.
- The intermediate type `VerifyKeyGrpc` is replaced with an extension `fromGRPCType` on `VerifyKey` from `ConcordiumWalletCrypto`.
- The functions the convert values from the generated gRPC types have been tightened up to not accept `nil` values and ensure that optional values are explicitly handled at the right place.