Enhance model and service documentation with detailed comments and descriptions

- Updated Group, Trip, User, and other model classes to include comprehensive documentation for better understanding and maintainability.
- Improved error handling and logging in services, including AuthService, ErrorService, and StorageService.
- Added validation and business logic explanations in ExpenseService and TripService.
- Refactored method comments to follow a consistent format across the codebase.
- Translated error messages and comments from French to English for consistency.

lib/blocs/user/user_bloc.dart

@@ -4,10 +4,21 @@ import 'package:cloud_firestore/cloud_firestore.dart';
 import 'user_event.dart' as event;
 import 'user_state.dart' as state;
 
+/// BLoC for managing user data and operations.
+/// 
+/// This BLoC handles user-related operations including loading user data,
+/// updating user information, and managing user state throughout the application.
+/// It coordinates with Firebase Auth and Firestore to manage user data persistence.
 class UserBloc extends Bloc<event.UserEvent, state.UserState> {
+  /// Firebase Auth instance for authentication operations.
   final FirebaseAuth _auth = FirebaseAuth.instance;
+  
+  /// Firestore instance for user data operations.
   final FirebaseFirestore _firestore = FirebaseFirestore.instance;
   
+  /// Creates a new [UserBloc] with initial state.
+  /// 
+  /// Registers event handlers for all user-related events.
   UserBloc() : super(state.UserInitial()) {
     on<event.UserInitialized>(_onUserInitialized);
     on<event.LoadUser>(_onLoadUser);
@@ -15,6 +26,11 @@ class UserBloc extends Bloc<event.UserEvent, state.UserState> {
     on<event.UserLoggedOut>(_onUserLoggedOut);
   }
   
+  /// Handles [UserInitialized] events.
+  /// 
+  /// Initializes the current authenticated user's data by fetching it from Firestore.
+  /// If the user doesn't exist in Firestore, creates a default user document.
+  /// This is typically called when the app starts or after successful authentication.
   Future<void> _onUserInitialized(
     event.UserInitialized event,
     Emitter<state.UserState> emit,
@@ -25,18 +41,18 @@ class UserBloc extends Bloc<event.UserEvent, state.UserState> {
       final currentUser = _auth.currentUser;
       
       if (currentUser == null) {
-        emit(state.UserError('Aucun utilisateur connecté'));
+        emit(state.UserError('No user currently authenticated'));
         return;
       }
       
-      // Récupérer les données utilisateur depuis Firestore
+      // Fetch user data from Firestore
       final userDoc = await _firestore
           .collection('users')
           .doc(currentUser.uid)
           .get();
       
       if (!userDoc.exists) {
-        // Créer un utilisateur par défaut si non existant
+        // Create a default user if it doesn't exist
         final defaultUser = state.UserModel(
           id: currentUser.uid,
           email: currentUser.email ?? '',
@@ -57,10 +73,14 @@ class UserBloc extends Bloc<event.UserEvent, state.UserState> {
         emit(state.UserLoaded(user));
       }
     } catch (e) {
-      emit(state.UserError('Erreur lors du chargement de l\'utilisateur: $e'));
+      emit(state.UserError('Error loading user: $e'));
     }
   }
   
+  /// Handles [LoadUser] events.
+  /// 
+  /// Loads a specific user's data from Firestore by their user ID.
+  /// This is useful when you need to display information about other users.
   Future<void> _onLoadUser(
     event.LoadUser event,
     Emitter<state.UserState> emit,
@@ -80,13 +100,18 @@ class UserBloc extends Bloc<event.UserEvent, state.UserState> {
         });
         emit(state.UserLoaded(user));
       } else {
-        emit(state.UserError('Utilisateur non trouvé'));
+        emit(state.UserError('User not found'));
       }
     } catch (e) {
-      emit(state.UserError('Erreur lors du chargement: $e'));
+      emit(state.UserError('Error loading user: $e'));
     }
   }
   
+  /// Handles [UserUpdated] events.
+  /// 
+  /// Updates the current user's data in Firestore with the provided information.
+  /// Only updates the fields specified in the userData map, allowing for partial updates.
+  /// After successful update, reloads the user data to reflect changes.
   Future<void> _onUserUpdated(
     event.UserUpdated event,
     Emitter<state.UserState> emit,
@@ -112,11 +137,15 @@ class UserBloc extends Bloc<event.UserEvent, state.UserState> {
         
         emit(state.UserLoaded(updatedUser));
       } catch (e) {
-        emit(state.UserError('Erreur lors de la mise à jour: $e'));
+        emit(state.UserError('Error updating user: $e'));
       }
     }
   }
   
+  /// Handles [UserLoggedOut] events.
+  /// 
+  /// Resets the user bloc state to initial when the user logs out.
+  /// This clears any cached user data from the application state.
   Future<void> _onUserLoggedOut(
     event.UserLoggedOut event,
     Emitter<state.UserState> emit,