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/components/count/group_expenses_page.dart

@@ -0,0 +1,116 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_bloc/flutter_bloc.dart';
+import '../../blocs/count/count_bloc.dart';
+import '../../blocs/count/count_event.dart';
+import '../../blocs/count/count_state.dart';
+import '../../blocs/user/user_bloc.dart';
+import '../../blocs/user/user_state.dart' as user_state;
+import '../../data/models/group.dart';
+import 'add_expense_dialog.dart';
+import 'balances_tab.dart';
+import 'expenses_tab.dart';
+import 'settlements_tab.dart';
+
+class GroupExpensesPage extends StatefulWidget {
+  final Group group;
+
+  const GroupExpensesPage({
+    super.key,
+    required this.group,
+  });
+
+  @override
+  State<GroupExpensesPage> createState() => _GroupExpensesPageState();
+}
+
+class _GroupExpensesPageState extends State<GroupExpensesPage>
+    with SingleTickerProviderStateMixin {
+  late TabController _tabController;
+
+  @override
+  void initState() {
+    super.initState();
+    _tabController = TabController(length: 3, vsync: this);
+    context.read<CountBloc>().add(LoadExpenses(widget.group.id));
+  }
+
+  @override
+  void dispose() {
+    _tabController.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(widget.group.name),
+        bottom: TabBar(
+          controller: _tabController,
+          tabs: const [
+            Tab(text: 'Dépenses', icon: Icon(Icons.receipt_long)),
+            Tab(text: 'Balances', icon: Icon(Icons.account_balance)),
+            Tab(text: 'Remboursements', icon: Icon(Icons.payments)),
+          ],
+        ),
+      ),
+      body: BlocConsumer<CountBloc, CountState>(
+        listener: (context, state) {
+          if (state is CountError) {
+            ScaffoldMessenger.of(context).showSnackBar(
+              SnackBar(
+                content: Text(state.message),
+                backgroundColor: Colors.red,
+              ),
+            );
+          }
+        },
+        builder: (context, state) {
+          if (state is CountLoading) {
+            return const Center(child: CircularProgressIndicator());
+          }
+
+          if (state is ExpensesLoaded) {
+            return TabBarView(
+              controller: _tabController,
+              children: [
+                ExpensesTab(
+                  expenses: state.expenses,
+                  group: widget.group,
+                ),
+                BalancesTab(balances: state.balances),
+                SettlementsTab(settlements: state.settlements),
+              ],
+            );
+          }
+
+          return const Center(child: Text('Aucune donnée'));
+        },
+      ),
+      floatingActionButton: BlocBuilder<UserBloc, user_state.UserState>(
+        builder: (context, userState) {
+          if (userState is! user_state.UserLoaded) return const SizedBox();
+
+          return FloatingActionButton.extended(
+            onPressed: () => _showAddExpenseDialog(context, userState.user),
+            icon: const Icon(Icons.add),
+            label: const Text('Dépense'),
+          );
+        },
+      ),
+    );
+  }
+
+  void _showAddExpenseDialog(BuildContext context, user_state.UserModel currentUser) {
+    showDialog(
+      context: context,
+      builder: (dialogContext) => BlocProvider.value(
+        value: context.read<CountBloc>(),
+        child: AddExpenseDialog(
+          group: widget.group,
+          currentUser: currentUser,
+        ),
+      ),
+    );
+  }
+}