refactor: included initial factory constructor

lib/game/bloc/game_bloc.dart

@@ -6,7 +6,7 @@ part 'game_event.dart';
 part 'game_state.dart';
 
 class GameBloc extends Bloc<GameEvent, GameState> {
-  GameBloc() : super(const GameState(score: 0, balls: 3)) {
+  GameBloc() : super(GameState.initial()) {
     on<BallLost>(_onBallLost);
     on<Scored>(_onScored);
   }

lib/game/bloc/game_state.dart

@@ -11,6 +11,11 @@ class GameState extends Equatable {
   })  : assert(score >= 0, "Score can't be negative"),
         assert(balls >= 0, "Number of balls can't be negative");
 
+  factory GameState.initial() => const GameState(
+        score: 0,
+        balls: 3,
+      );
+
   /// The current score of the game.
   final int score;