refactor: Enable lint use_build_context_synchronously

lib/pages/chat/events/audio_player.dart

@@ -189,6 +189,7 @@ class AudioPlayerState extends State<AudioPlayerWidget> {
       });
     } catch (e, s) {
       Logs().v('Could not download audio file', e, s);
+      if (!mounted) rethrow;
       ScaffoldMessenger.of(
         context,
       ).showSnackBar(SnackBar(content: Text(e.toLocalizedString(context))));
@@ -208,6 +209,7 @@ class AudioPlayerState extends State<AudioPlayerWidget> {
         ),
       );
     }
+    if (!mounted) return;
 
     audioPlayer.play().onError(
       ErrorReporter(context, 'Unable to play audio message').onErrorCallback,

lib/pages/chat/events/cute_events.dart

@@ -50,6 +50,7 @@ class _CuteContentState extends State<CuteContent> {
   Future<void> addOverlay() async {
     _isOverlayShown = true;
     await Future.delayed(const Duration(milliseconds: 50));
+    if (!mounted) return;
 
     OverlayEntry? overlay;
     overlay = OverlayEntry(

lib/pages/chat/events/message_content.dart

@@ -61,9 +61,11 @@ class MessageContent extends StatelessWidget {
     final client = Matrix.of(context).client;
     final state = await client.getCryptoIdentityState();
     if (!state.connected) {
+      if (!context.mounted) return;
       final success = await context.push('/backup');
       if (success != true) return;
     }
+    if (!context.mounted) return;
     event.requestKey();
     final sender = event.senderFromMemoryOrFallback;
     await showAdaptiveBottomSheet(