Fixes #4389 - Add comprehensive unit tests for WindowsKeyConverter (#4390)

* Add comprehensive unit tests for WindowsKeyConverter

- Implement 118 parallelizable unit tests for WindowsKeyConverter

- Cover ToKey and ToKeyInfo methods with full bidirectional testing

- Test basic characters, modifiers, special keys, function keys

- Test VK_PACKET Unicode/IME input

- Test OEM keys, NumPad keys, and lock states

- Include round-trip conversion tests

- All tests passing successfully

Fixes #4389

* Add test documenting VK_PACKET surrogate pair limitation

VK_PACKET sends surrogate pairs (e.g., emoji) as two separate events. Current WindowsKeyConverter processes each independently without combining. Test documents this limitation for future fix at InputProcessor level.

* Mark WindowsKeyConverterTests as Windows-only

Tests now skip on non-Windows platforms using SkipException in constructor. This prevents CI failures on macOS and Linux where Windows Console API is not available.

* Properly mark WindowsKeyConverter tests as Windows-only

Created custom xUnit attributes SkipOnNonWindowsFact and SkipOnNonWindowsTheory that automatically skip tests on non-Windows platforms. This prevents CI failures on macOS and Linux.

* Refactor and enhance test coverage for input processors

Refactored `ApplicationImpl.cs` to simplify its structure by removing the `_stopAfterFirstIteration` field. Reintroduced and modernized test files with improved structure and coverage:

- `NetInputProcessorTests.cs`: Added tests for `ConsoleKeyInfo` to `Rune`/`Key` conversion and queue processing.
- `WindowSizeMonitorTests.cs`: Added tests for size change event handling.
- `WindowsInputProcessorTests.cs`: Added tests for keyboard and mouse input processing, including mouse flag mapping.
- `WindowsKeyConverterTests.cs`: Added comprehensive tests for `InputRecord` to `Key` conversion, covering OEM keys, modifiers, Unicode, and round-trip integrity.

Improved test coverage for edge cases, introduced parameterized tests, and documented known limitations for future improvements.

* Use Trait-based platform filtering for WindowsKeyConverter tests

Added [Trait('Platform', 'Windows')] and [Collection('Global Test Setup')] attributes. Tests will run on Windows but can be filtered in CI on other platforms using --filter 'Platform!=Windows' if needed. This approach doesn't interfere with GlobalTestSetup and works correctly with xUnit.

* Filter Windows-specific tests on non-Windows CI platforms

Added --filter 'Platform!=Windows' for Linux and macOS runners to exclude WindowsKeyConverterTests which require Windows Console APIs. Windows runner runs all tests normally.

* Fix log path typo and remove Codecov upload step

Corrected a typo in the log directory path from
`logs/UnitTestsParallelable/` to `logs/UnitTestsParallelizable/`.
Removed the "Upload Parallelizable UnitTests Coverage to Codecov"
step, which was conditional on `matrix.os == 'ubuntu-latest'`
and used the `codecov/codecov-action@v4` action. This change
improves log handling and removes the Codecov integration.

* Refactor application reset logic

Replaced `Application.ResetState(true)` with a more explicit reset
mechanism. Introduced `ApplicationImpl.SetInstance(null)` to clear
the application instance and added `CM.Disable(true)` to disable
specific components. This change improves control over the reset
process and ensures a more granular approach to application state
management.

* Improve null safety with ?. and ! operators

Enhanced null safety across the codebase by introducing the null-conditional operator (`?.`) and null-forgiving operator (`!`) where appropriate.

- Updated `app` and `driver` method calls to use `?.` to prevent potential `NullReferenceException` errors.
- Added `!` to assert non-nullability in cases like `e.Value!.ToString()` and `app.Driver?.Contents!`.
- Modified `lv.SelectedItemChanged` event handler to ensure safe handling of nullable values.
- Updated `app.Shutdown()`, `app.LayoutAndDraw()`, and mouse event handling to use `?.`.
- Ensured `driver.SetScreenSize` is invoked only when `driver` is not null.
- Improved string concatenation logic with null-forgiving operator for `Contents`.
- General improvements to null safety to make the code more robust and resilient to null references.

* Improve Unicode tests and clarify surrogate pair handling

Updated `WindowsKeyConverterTests` to enhance readability, improve test data, and clarify comments. Key changes include:

- Reformatted `[Collection]` and `[Trait]` attributes for consistency.
- Replaced placeholder Unicode characters with meaningful examples:
  - Chinese: `中`, Japanese: `日`, Korean: `한`, Accented: `é`, Euro: `€`, Greek: `Ω`.
- Updated comments to replace placeholder emojis (`??`) with `😀` (U+1F600) for clarity.
- Adjusted surrogate pair test data to accurately reflect `😀`.
- Improved documentation of current limitations and future fixes for surrogate pair handling.

These changes ensure more accurate and meaningful test cases while improving code clarity.

* Ensure platform-specific test execution on Windows

Added `System.Runtime.InteropServices` and `Xunit.Sdk` namespaces to `WindowsKeyConverterTests.cs` to support platform checks and test setup. Marked the test class with `[Collection("Global Test Setup")]` to enable shared test setup. Updated the `ToKey_NumPadKeys_ReturnsExpectedKeyCode` method to include a platform check, ensuring the test only runs on Windows platforms.

* Integrate TrueColor support into ColorPicker

Merged TrueColors functionality into ColorPicker, enhancing the scenario with TrueColor demonstration and gradient features. Updated `ColorPicker.cs` to include driver information, TrueColor support indicators, and a toggle for `Force16Colors`. Removed `TrueColors.cs` as its functionality is now consolidated.

Refined `ColorBar` to use dynamic height with `Dim.Auto` for better flexibility. Added documentation to `HueBar` to clarify its role in representing the Hue component in HSL color space.

* Revert workflow change.

* Reverted attribute that didn't actualy work.

Tests/IntegrationTests/UICatalog/ScenarioTests.cs

@@ -35,7 +35,9 @@ public class ScenarioTests : TestsAllViews
             return;
         }
 
-        Application.ResetState (true);
+        // Force a complete reset
+        ApplicationImpl.SetInstance (null);
+        CM.Disable (true);
 
         _output.WriteLine ($"Running Scenario '{scenarioType}'");
         Scenario? scenario = null;