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/auth/auth_state.dart

@@ -1,40 +1,75 @@
 import 'package:equatable/equatable.dart';
 import '../../models/user.dart';
 
+/// Abstract base class for all authentication states.
+/// 
+/// This class extends [Equatable] to enable value equality for state comparison.
+/// All authentication states in the application should inherit from this class.
 abstract class AuthState extends Equatable {
+  /// Creates a new [AuthState].
   const AuthState();
 
   @override
   List<Object?> get props => [];
 }
 
+/// Initial state of the authentication bloc.
+/// 
+/// This state represents the initial state before any authentication
+/// actions have been performed.
 class AuthInitial extends AuthState {}
 
+/// State indicating that an authentication operation is in progress.
+/// 
+/// This state is used to show loading indicators during authentication
+/// processes like sign-in, sign-up, or sign-out.
 class AuthLoading extends AuthState {}
 
+/// State indicating that a user is successfully authenticated.
+/// 
+/// This state contains the authenticated user's information and is
+/// used throughout the app to access user data.
 class AuthAuthenticated extends AuthState {
+  /// The authenticated user.
   final User user;
 
+  /// Creates an [AuthAuthenticated] state with the given [user].
   const AuthAuthenticated({required this.user});
 
   @override
   List<Object?> get props => [user];
 }
 
+/// State indicating that no user is currently authenticated.
+/// 
+/// This state is used when a user is not signed in or has signed out
+/// of the application.
 class AuthUnauthenticated extends AuthState {}
 
+/// State indicating that an authentication error has occurred.
+/// 
+/// This state contains an error message that can be displayed to the user
+/// when authentication operations fail.
 class AuthError extends AuthState {
+  /// The error message describing what went wrong.
   final String message;
 
+  /// Creates an [AuthError] state with the given error [message].
   const AuthError({required this.message});
 
   @override
   List<Object?> get props => [message];
 }
 
+/// State indicating that a password reset email has been sent.
+/// 
+/// This state is used to confirm to the user that a password reset
+/// email has been successfully sent to their email address.
 class AuthPasswordResetSent extends AuthState {
+  /// The email address to which the reset link was sent.
   final String email;
 
+  /// Creates an [AuthPasswordResetSent] state with the given [email].
   const AuthPasswordResetSent({required this.email});
 
   @override