refactor: update providers to use keepAlive for enhanced state management

- Changed multiple provider annotations to `@Riverpod(keepAlive: true)` to improve state retention and management across the application.
- This update aligns with recent enhancements in state management practices, ensuring better performance and user experience throughout the app.

lib/features/chat/services/message_batch_service.dart

@@ -534,7 +534,7 @@ final selectedMessagesProvider =
     );
 
 /// Provider for batch operation mode
-@riverpod
+@Riverpod(keepAlive: true)
 class BatchMode extends _$BatchMode {
   @override
   bool build() => false;

lib/features/chat/services/voice_input_service.dart

@@ -326,7 +326,7 @@ final voiceInputServiceProvider = Provider<VoiceInputService>((ref) {
   return VoiceInputService();
 });
 
-@riverpod
+@Riverpod(keepAlive: true)
 Future<bool> voiceInputAvailable(Ref ref) async {
   final service = ref.watch(voiceInputServiceProvider);
   if (!service.isSupportedPlatform) return false;