[macOS] [version 0.4.3]: unexpectedly found nil while unwrapping an Optional value

Nobody has claimed this yet.

Getting this error when trying to perform a redirect to my auth:

`flutter_web_auth/FlutterWebAuthPlugin.swift:38: Fatal error: Unexpectedly found nil while unwrapping an Optional value`

Tried looking at the code in question, but unfamiliar with Swift, seems to be that ``keyWindow`` is null? Is there any setup step for macOS that is needed before using this library?

```swift
guard let provider = NSApplication.shared.keyWindow!.contentViewController as? FlutterViewController else {
result(FlutterError(code: "FAILED", message: "Failed to aquire root FlutterViewController" , details: nil))
return
}
```

flutter doctor output:
```
~/$ flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.10.1, on macOS 13.3.1 22E772610a darwin-arm64, locale en-PT)
[✓] Android toolchain - develop for Android devices (Android SDK version 33.0.0)
[✓] Xcode - develop for iOS and macOS (Xcode 14.3)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2021.2)
[✓] IntelliJ IDEA Ultimate Edition (version 2022.1.3)
[✓] VS Code (version 1.78.1)
[✓] Connected device (2 available)
[✓] Network resources

• No issues found!
```

Start in flutter_web_auth/FlutterWebAuthPlugin.swift at line 38 and review the macOS authentication redirect path around the keyWindow access. Reproduce the redirect with the reported Flutter 3.10.1 and macOS setup, then add or update a focused test or validation so the authentication flow no longer crashes when the expected window or controller is unavailable.

Written by the indexing model from the issue text.