stop playing media if we seek to an asset that is not remote

mobile/lib/interfaces/cast_destination_service.interface.dart

@@ -20,6 +20,7 @@ abstract interface class ICastDestinationService {
   void play();
   void pause();
   void seekTo(Duration position);
+  void stop();
   Future<void> disconnect();
 
   Future<List<(String, CastDestinationType, dynamic)>> getDevices();

mobile/lib/pages/common/gallery_viewer.page.dart

@@ -130,6 +130,7 @@ class GalleryViewerPage extends HookConsumerWidget {
         if (isCasting) {
           WidgetsBinding.instance.addPostFrameCallback((_) {
             if (context.mounted) {
+              ref.read(castProvider.notifier).stop();
               context.scaffoldMessenger.showSnackBar(
                 SnackBar(
                   duration: const Duration(seconds: 1),
@@ -398,6 +399,7 @@ class GalleryViewerPage extends HookConsumerWidget {
                   context.scaffoldMessenger.clearSnackBars();
 
                   if (isCasting) {
+                    ref.read(castProvider.notifier).stop();
                     context.scaffoldMessenger.showSnackBar(
                       SnackBar(
                         duration: const Duration(seconds: 2),

mobile/lib/providers/cast.provider.dart

@@ -83,6 +83,10 @@ class CastNotifier extends StateNotifier<CastManagerState> {
     _gCastService.seekTo(position);
   }
 
+  void stop() {
+    _gCastService.stop();
+  }
+
   Future<void> disconnect() async {
     await _gCastService.disconnect();
   }

mobile/lib/services/gcast.service.dart

@@ -263,6 +263,17 @@ class GCastService implements ICastDestinationService {
     });
   }
 
+  @override
+  void stop() {
+    _gCastRepository.sendMessage(CastSession.kNamespaceMedia, {
+      "type": "STOP",
+      "mediaSessionId": _sessionId,
+    });
+    _mediaStatusPollingTimer?.cancel();
+
+    currentAssetId = null;
+  }
+
   @override
   Future<List<(String, CastDestinationType, dynamic)>> getDevices() async {
     final dests = await _gCastRepository.listDestinations();