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/data/models/group.dart

@@ -0,0 +1,26 @@
+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,
+    };
+  }
+}