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/services/trip_service.dart

@@ -1,10 +1,42 @@
+/// A service that handles trip-related business logic and data operations.
+///
+/// This service provides functionality for:
+/// - Trip creation, updating, and deletion
+/// - Trip validation and business rule enforcement
+/// - Location-based trip suggestions
+/// - Trip statistics and analytics
+/// - Integration with Firebase Firestore for data persistence
+///
+/// The service ensures data integrity by validating trip information
+/// before database operations and provides comprehensive error handling
+/// and logging through the ErrorService.
+///
+/// Example usage:
+/// ```dart
+/// final tripService = TripService();
+/// 
+/// // Create a new trip
+/// final tripId = await tripService.createTrip(newTrip);
+/// 
+/// // Get trip suggestions for a location
+/// final suggestions = await tripService.getTripSuggestions('Paris');
+/// 
+/// // Calculate trip statistics
+/// final stats = await tripService.getTripStatistics(tripId);
+/// ```
 import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:travel_mate/services/error_service.dart';
 import '../models/trip.dart';
 
+/// Service for managing trip-related operations and business logic.
 class TripService {
+  /// Service for error handling and logging
   final _errorService = ErrorService();
+  
+  /// Firestore instance for database operations
   final FirebaseFirestore _firestore = FirebaseFirestore.instance;
+  
+  /// Collection name for trips in Firestore
   static const String _tripsCollection = 'trips';
 
   // Charger tous les voyages