Refactor menu rendering and improve projection sampling

- Updated AsciiRasterizer to support game and episode selection menus with improved layout and cursor handling.
- Enhanced SixelRasterizer and SoftwareRasterizer to modularize menu drawing logic for game and episode selection.
- Introduced new methods for drawing menus and applying fade effects across rasterizers.
- Adjusted wall texture sampling in Rasterizer to anchor to projection height center for consistent rendering.
- Added tests for wall texture sampling behavior to ensure legacy compatibility and new functionality.
- Modified Flutter audio adapter to use nullable access for active game and adjusted game selection logic in the main class.
- Cleaned up input handling in Wolf3dFlutterInput by removing unused menu tap variables.

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

packages/wolf_3d_flutter/lib/audio/audio_adaptor.dart

@@ -43,7 +43,7 @@ class FlutterAudioAdapter implements EngineAudio {
   }
 
   @override
-  WolfensteinData? get activeGame => wolf3d.activeGame;
+  WolfensteinData? get activeGame => wolf3d.maybeActiveGame;
 
   @override
   set activeGame(WolfensteinData? value) {