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_state.dart

@@ -0,0 +1,21 @@
+import 'package:equatable/equatable.dart';
+import 'package:flutter/material.dart';
+
+class ThemeState extends Equatable {
+  final ThemeMode themeMode;
+
+  const ThemeState({this.themeMode = ThemeMode.system});
+
+  bool get isDarkMode {
+    return themeMode == ThemeMode.dark;
+  }
+
+  ThemeState copyWith({ThemeMode? themeMode}) {
+    return ThemeState(
+      themeMode: themeMode ?? this.themeMode,
+    );
+  }
+
+  @override
+  List<Object?> get props => [themeMode];
+}