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/blocs/trip/trip_state.dart

@@ -0,0 +1,40 @@
+import 'package:equatable/equatable.dart';
+import '../../data/models/trip.dart';
+
+abstract class TripState extends Equatable {
+  const TripState();
+
+  @override
+  List<Object?> get props => [];
+}
+
+class TripInitial extends TripState {}
+
+class TripLoading extends TripState {}
+
+class TripLoaded extends TripState {
+  final List<Trip> trips;
+
+  const TripLoaded({required this.trips});
+
+  @override
+  List<Object?> get props => [trips];
+}
+
+class TripOperationSuccess extends TripState {
+  final String message;
+
+  const TripOperationSuccess({required this.message});
+
+  @override
+  List<Object?> get props => [message];
+}
+
+class TripError extends TripState {
+  final String message;
+
+  const TripError({required this.message});
+
+  @override
+  List<Object?> get props => [message];
+}