feat: Add library directive to multiple BLoC and service files for improved organization

lib/blocs/balance/balance_bloc.dart

@@ -31,6 +31,7 @@
 ///   amount: 50.0,
 /// ));
 /// ```
+library;
 import 'package:flutter_bloc/flutter_bloc.dart';
 import '../../repositories/balance_repository.dart';
 import '../../repositories/expense_repository.dart';