Pubspec constructor
      const
      Pubspec({ 
    
    
- required String packageName,
- required Map<String, VersionConstraint?> environment,
- required FlutterGen flutterGen,
- required Flutter flutter,
Implementation
const Pubspec({
  required this.packageName,
  required this.environment,
  required this.flutterGen,
  required this.flutter,
});