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/theme/theme_event.dart

@@ -0,0 +1,20 @@
+import 'package:equatable/equatable.dart';
+import 'package:flutter/material.dart';
+
+abstract class ThemeEvent extends Equatable {
+  const ThemeEvent();
+
+  @override
+  List<Object?> get props => [];
+}
+
+class ThemeChanged extends ThemeEvent {
+  final ThemeMode themeMode;
+
+  const ThemeChanged({required this.themeMode});
+
+  @override
+  List<Object?> get props => [themeMode];
+}
+
+class ThemeLoadRequested extends ThemeEvent {}