feat: Implement audio backend with subprocess support and refactor audio handling

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

apps/wolf_3d_gui/lib/screens/audio_gallery.dart

@@ -5,7 +5,6 @@ import 'dart:async';
 
 import 'package:flutter/material.dart';
 import 'package:wolf_3d_dart/wolf_3d_data_types.dart';
-import 'package:wolf_3d_dart/wolf_3d_synth.dart';
 import 'package:wolf_3d_flutter/wolf_3d_flutter.dart';
 import 'package:wolf_3d_gui/screens/gallery_game_selector.dart';
 
@@ -142,15 +141,16 @@ class _AudioGalleryState extends State<AudioGallery> {
     }
 
     final engineAudio = widget.wolf3d.audio;
-    if (engineAudio is! WolfAudio) {
+    if (engineAudio is! DebugMusicPlayer) {
       return;
     }
+    final debugAudio = engineAudio as DebugMusicPlayer;
 
     if (trackIndex < 0 || trackIndex >= _selectedGame.music.length) {
       return;
     }
 
-    await engineAudio.playMusic(_selectedGame.music[trackIndex]);
+    await debugAudio.playMusic(_selectedGame.music[trackIndex]);
     if (!mounted) {
       return;
     }