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/models/group.dart

@@ -1,26 +0,0 @@
-class Group {
-  final String? id;
-  final String name;
-  final List<String> members;
-
-  Group({
-    this.id,
-    required this.name,
-    required this.members,
-  });
-
-  factory Group.fromMap(Map<String, dynamic> data, String documentId) {
-    return Group(
-      id: documentId,
-      name: data['name'] ?? '',
-      members: List<String>.from(data['members'] ?? []),
-    );
-  }
-
-  Map<String, dynamic> toMap() {
-    return {
-      'name': name,
-      'members': members,
-    };
-  }
-}