feat: Implement audio shutdown procedure for graceful app exit

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

apps/wolf_3d_gui/lib/screens/game_screen.dart

@@ -143,7 +143,6 @@ class _GameScreenState extends State<GameScreen> {
       DefaultRendererSettingsPersistence();
   final DefaultSaveGamePersistence _savePersistence =
       DefaultSaveGamePersistence();
-  Future<void>? _audioShutdownFuture;
 
   /// Mirrors [WolfRendererSettings.mode] into the Flutter renderer enum.
   RendererMode _rendererMode = RendererMode.hardware;
@@ -213,29 +212,15 @@ class _GameScreenState extends State<GameScreen> {
 
   @override
   void dispose() {
-    unawaited(_shutdownAudioForExit());
+    unawaited(widget.wolf3d.shutdownAudio());
     super.dispose();
   }
 
   Future<void> _quitApplication() async {
-    await _shutdownAudioForExit();
+    await widget.wolf3d.shutdownAudio();
     await SystemNavigator.pop();
   }
 
-  Future<void> _shutdownAudioForExit() {
-    final existing = _audioShutdownFuture;
-    if (existing != null) {
-      return existing;
-    }
-
-    final shutdown = () async {
-      await widget.wolf3d.audio.stopAllAudio();
-      widget.wolf3d.audio.dispose();
-    }();
-    _audioShutdownFuture = shutdown;
-    return shutdown;
-  }
-
   @override
   Widget build(BuildContext context) {
     return PopScope(