fix(voice-call): Improve async handling and state management

Refactor voice call service to handle asynchronous operations more
precisely. Update method signatures to be async, use unawaited for
non-blocking calls, and ensure proper state reset between sessions.
Improve error handling and resource management for voice input and
text-to-speech services.

lib/features/chat/services/voice_input_service.dart

@@ -1026,12 +1026,12 @@ class VoiceInputService {
     });
   }
 
-  void dispose() {
-    stopListening();
-    unawaited(_disposeVadHandler());
-    unawaited(_microphonePermissionProbe.dispose());
+  Future<void> dispose() async {
+    await stopListening();
+    await _disposeVadHandler();
+    await _microphonePermissionProbe.dispose();
     try {
-      _speech.stop();
+      await _speech.stop();
     } catch (_) {}
   }
 }