feat: Remove triggerQuitOnInitForTest from GameScreen and add audio shutdown test

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

apps/wolf_3d_gui/lib/screens/game_screen.dart

@@ -135,10 +135,6 @@ class GameScreen extends StatefulWidget {
   @visibleForTesting
   final bool skipEngineBootstrapForTest;
 
-  /// Triggers the quit flow during init for deterministic widget tests.
-  @visibleForTesting
-  final bool triggerQuitOnInitForTest;
-
   /// Creates a gameplay screen driven by [wolf3d].
   const GameScreen({
     required this.wolf3d,
@@ -146,7 +142,6 @@ class GameScreen extends StatefulWidget {
     this.hostShortcutRegistry = HostShortcutRegistry.defaults,
     this.appExitHandler,
     this.skipEngineBootstrapForTest = false,
-    this.triggerQuitOnInitForTest = false,
     super.key,
   });
 
@@ -169,9 +164,6 @@ class _GameScreenState extends State<GameScreen> {
   void initState() {
     super.initState();
     if (widget.skipEngineBootstrapForTest) {
-      if (widget.triggerQuitOnInitForTest) {
-        unawaited(_quitApplication());
-      }
       return;
     }