refactor: adopt Dart 3.9 features and migrate the example integration tests to patrol

[spydon]

Summary

The minimum Dart SDK was bumped to 3.9.0, so this modernizes hand-written code to the newly available language features. That bump, together with the recent pub workspace migration, also broke the pipeline, so this pull request additionally replaces the example's Appium end to end suite with patrol and gets every workflow green again. All of the source changes are behavior preserving.

Dart 3.9 language features

Switch statements to switch expressions:

• field.dart, corbado.dart (_convertFirebaseFunctionsException), and the three fromPlatformType factories in passkeyLoginRequest.dart
• corbado_auth_component.dart, the screenName builder switch
• The two availableFallbacks.length switches in passkey_verify_block.dart and passkey_append_block.dart
• The example router.dart redirect switch, using when guards

Pattern matching with when guards, which removes two // ignore: no_default_cases comments:

• The alternative.type switches in both block files

Record destructuring with a switch expression:

• debug_overlay.dart, now final (IconData iconData, Color color) = switch (cp.type) { ... }

Null-aware map entries:

• authenticate_request.dart and register_request.dart toJson(), where if (x != null) 'k': x becomes 'k': ?x

The switches in authenticator.dart, process_handler.dart, and ExceptionFactory.fromBackendMessage were left as statements because converting them would hurt readability. Generated API client packages were not touched.

Example integration tests, Appium to patrol

The pub workspace now resolves all members together, and the example's appium_flutter_server development dependency pulled in shelf_plus, which could not co-resolve and broke melos bootstrap. The JavaScript Appium suite is replaced with patrol:

• Removed appium_flutter_server and the tests/ JavaScript directory, and added patrol with its patrol configuration block.
• Added integration_test/passkeys_test.dart covering navigation, every sign up and login configuration, and the error shown when logging in without a passkey. The two passkey ceremonies (default sign up and default login) are included but skipped unless RUN_CEREMONIES is set, because patrol cannot match a biometric prompt on its own.
• Added the Android instrumentation runner and build.gradle setup, and removed the flutter_driver test hook from main.dart.
• Documented the patrol workflow in the example README.

Pipeline

• Bumped the Flutter version in the main workflows to 3.44.5. The code generation toolchain (pigeon, source_gen, build_runner) requires analyzer 8 or newer, which needs Dart 3.10 or newer. These are development dependencies only, so the published sdk: ">=3.9.0" support for consumers is unchanged.
• Disabled Jetifier for the Android example build, since the project is fully AndroidX, and bumped the Android NDK to 28.2.13676358, which integration_test requires.
• Built the macOS example without code signing, since the runner has no signing identity.
• Added a separate integration-test workflow that runs the patrol suite on an Android emulator. It uses Flutter 3.41.x, because patrol cannot build on 3.44.5 and 3.38.x cannot resolve the workspace. It runs only on pull requests whose title starts with chore(release): (or a manual dispatch), is bounded by a timeout, and is currently non-gating. The passkey ceremonies are opt in through a run_ceremonies dispatch input, backed by a screen-lock PIN and a host side adb emu finger loop.

Verification

• melos format --set-exit-if-changed passes.
• melos analyze --fatal-infos passes.
• melos test passes.
• The main pipeline is green across all seven jobs. The integration-test job passes on the emulator, with all six deterministic tests passing and the two ceremonies skipped as designed.