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/balance/balance_event.dart

@@ -1,36 +1,68 @@
 import 'package:equatable/equatable.dart';
 
+/// Abstract base class for all balance-related events.
+/// 
+/// This class extends [Equatable] to enable value equality for event comparison.
+/// All balance events in the application should inherit from this class.
 abstract class BalanceEvent extends Equatable {
+  /// Creates a new [BalanceEvent].
   const BalanceEvent();
 
   @override
   List<Object?> get props => [];
 }
 
+/// Event to load balance information for a specific group.
+/// 
+/// This event triggers the loading of user balances and settlements
+/// for all members of the specified group. It calculates who owes
+/// money to whom based on shared expenses.
 class LoadGroupBalances extends BalanceEvent {
+  /// The ID of the group to load balances for.
   final String groupId;
   
+  /// Creates a [LoadGroupBalances] event for the specified [groupId].
   const LoadGroupBalances(this.groupId);
   
   @override
   List<Object> get props => [groupId];
 }
 
+/// Event to refresh balance calculations for a group.
+/// 
+/// This event recalculates all balances and settlements for a group,
+/// typically called after expenses are added, modified, or deleted.
 class RefreshBalance extends BalanceEvent {
+  /// The ID of the group to refresh balances for.
   final String groupId;
 
+  /// Creates a [RefreshBalance] event for the specified [groupId].
   const RefreshBalance(this.groupId);
 
   @override
   List<Object?> get props => [groupId];
 }
 
+/// Event to mark a settlement as completed between two users.
+/// 
+/// This event is dispatched when one user pays back money they owe
+/// to another user, updating the balance calculations accordingly.
 class MarkSettlementAsCompleted extends BalanceEvent {
+  /// The ID of the group where the settlement occurred.
   final String groupId;
+  
+  /// The ID of the user who is paying the debt.
   final String fromUserId;
+  
+  /// The ID of the user who is receiving the payment.
   final String toUserId;
+  
+  /// The amount being settled.
   final double amount;
 
+  /// Creates a [MarkSettlementAsCompleted] event with the settlement details.
+  /// 
+  /// All parameters are required to properly record the settlement.
   const MarkSettlementAsCompleted({
     required this.groupId,
     required this.fromUserId,