Refactor signup page to use BLoC pattern and implement authentication repository

- Updated signup.dart to replace Provider with BLoC for state management.
- Created AuthRepository to handle authentication logic and Firestore user management.
- Added TripRepository and UserRepository for trip and user data management.
- Implemented methods for user sign-in, sign-up, and data retrieval in repositories.
- Enhanced trip management with create, update, delete, and participant management functionalities.
- Updated AuthService to include new methods for sign-in and sign-up.
- Removed unnecessary print statements from TripService for cleaner code.
- Added dependencies for flutter_bloc and equatable in pubspec.yaml.

Not tested yet

lib/blocs/theme/theme_bloc.dart

@@ -0,0 +1,46 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'theme_event.dart';
+import 'theme_state.dart';
+
+class ThemeBloc extends Bloc<ThemeEvent, ThemeState> {
+  ThemeBloc() : super(const ThemeState()) {
+    on<ThemeChanged>(_onThemeChanged);
+    on<ThemeLoadRequested>(_onThemeLoadRequested);
+  }
+
+  Future<void> _onThemeChanged(
+    ThemeChanged event,
+    Emitter<ThemeState> emit,
+  ) async {
+    emit(state.copyWith(themeMode: event.themeMode));
+    
+    // Sauvegarder la préférence
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString('themeMode', event.themeMode.toString());
+  }
+
+  Future<void> _onThemeLoadRequested(
+    ThemeLoadRequested event,
+    Emitter<ThemeState> emit,
+  ) async {
+    final prefs = await SharedPreferences.getInstance();
+    final themeModeString = prefs.getString('themeMode');
+
+    if (themeModeString != null) {
+      ThemeMode themeMode;
+      switch (themeModeString) {
+        case 'ThemeMode.light':
+          themeMode = ThemeMode.light;
+          break;
+        case 'ThemeMode.dark':
+          themeMode = ThemeMode.dark;
+          break;
+        default:
+          themeMode = ThemeMode.system;
+      }
+      emit(state.copyWith(themeMode: themeMode));
+    }
+  }
+}