style: apply dart formatting fixes across lib/ and test/

11 files had formatting inconsistencies that caused the
--set-exit-if-changed gate to fail. Automated formatting
via dart format now passes cleanly.

lib/casting_business_object.dart

@@ -20,7 +20,7 @@ class CastingBusinessObject extends ChangeNotifier {
   CastingPlaybackStatus _playbackStatus = CastingPlaybackStatus.unknown;
   String? _connectedDeviceName;
   String? _lastError;
-  
+
   /// Callback for when native side requests local audio to stop
   VoidCallback? onStopLocalAudioRequested;