fix: prevent overlapping background music (#422)

* fix: prevent overlaping background music

* coverage

packages/pinball_audio/lib/src/pinball_audio.dart

@@ -116,6 +116,28 @@ class _LoopAudio extends _Audio {
   }
 }
 
+class _SingleLoopAudio extends _LoopAudio {
+  _SingleLoopAudio({
+    required PreCacheSingleAudio preCacheSingleAudio,
+    required LoopSingleAudio loopSingleAudio,
+    required String path,
+  }) : super(
+          preCacheSingleAudio: preCacheSingleAudio,
+          loopSingleAudio: loopSingleAudio,
+          path: path,
+        );
+
+  bool _playing = false;
+
+  @override
+  void play() {
+    if (!_playing) {
+      super.play();
+      _playing = true;
+    }
+  }
+}
+
 class _RandomABAudio extends _Audio {
   _RandomABAudio({
     required this.createAudioPool,
@@ -270,7 +292,7 @@ class PinballAudioPlayer {
         path: Assets.sfx.cowMoo,
         duration: const Duration(seconds: 2),
       ),
-      PinballAudio.backgroundMusic: _LoopAudio(
+      PinballAudio.backgroundMusic: _SingleLoopAudio(
         preCacheSingleAudio: _preCacheSingleAudio,
         loopSingleAudio: _loopSingleAudio,
         path: Assets.music.background,

packages/pinball_audio/test/src/pinball_audio_test.dart

@@ -447,6 +447,18 @@ void main() {
               .onCall('packages/pinball_audio/${Assets.music.background}'),
         ).called(1);
       });
+
+      test('plays only once', () async {
+        await Future.wait(audioPlayer.load());
+        audioPlayer
+          ..play(PinballAudio.backgroundMusic)
+          ..play(PinballAudio.backgroundMusic);
+
+        verify(
+          () => loopSingleAudio
+              .onCall('packages/pinball_audio/${Assets.music.background}'),
+        ).called(1);
+      });
     });
 
     test(