feat: Add expense management features with tabs for expenses, balances, and settlements

- Implemented ExpensesTab to display a list of expenses with details.
- Created GroupExpensesPage to manage group expenses with a tabbed interface.
- Added SettlementsTab to show optimized settlements between users.
- Developed data models for Expense and Balance, including necessary methods for serialization.
- Introduced CountRepository for Firestore interactions related to expenses.
- Added CountService to handle business logic for expenses and settlements.
- Integrated image picker for receipt uploads.
- Updated main.dart to include CountBloc and CountRepository.
- Enhanced pubspec.yaml with new dependencies for image picking and Firebase storage.

Not Tested yet

lib/main.dart

@@ -12,11 +12,13 @@ import 'blocs/theme/theme_state.dart';
 import 'blocs/group/group_bloc.dart';
 import 'blocs/user/user_bloc.dart';
 import 'blocs/trip/trip_bloc.dart';
+import 'blocs/count/count_bloc.dart';
 import 'repositories/auth_repository.dart';
 import 'repositories/trip_repository.dart';
 import 'repositories/user_repository.dart';
 import 'repositories/group_repository.dart';
 import 'repositories/message_repository.dart';
+import 'repositories/count_repository.dart';
 import 'pages/login.dart';
 import 'pages/home.dart';
 import 'pages/signup.dart';
@@ -52,6 +54,9 @@ class MyApp extends StatelessWidget {
         RepositoryProvider<MessageRepository>(
           create: (context) => MessageRepository(),
         ),
+        RepositoryProvider<CountRepository>(
+          create: (context) => CountRepository(),
+        ),
       ],
       child: MultiBlocProvider(
         providers: [
@@ -74,6 +79,9 @@ class MyApp extends StatelessWidget {
           BlocProvider(
             create: (context) => MessageBloc(),
             ),
+          BlocProvider(
+            create: (context) => CountBloc(),
+          ),
         ],
         child: BlocBuilder<ThemeBloc, ThemeState>(
           builder: (context, themeState) {