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/message.dart

@@ -1,15 +0,0 @@
-class Message {
-  final String text; 
-  final DateTime timestamp;
-  final String senderId;
-  final String senderName;
-  final String groupId;
-
-  Message({
-    required this.text,
-    required this.timestamp,
-    required this.senderId,
-    required this.senderName,
-    required this.groupId,
-  });
-}