refactor: removed children parameter

packages/pinball_components/lib/src/components/flapper/flapper.dart

@@ -31,9 +31,7 @@ class Flapper extends Component {
   ///
   /// This can be used for testing [Flapper]'s behaviors in isolation.
   @visibleForTesting
-  Flapper.test({
-    Iterable<Component>? children,
-  }) : super(children: children);
+  Flapper.test();
 }
 
 /// {@template flapper_entrance}

packages/pinball_components/test/src/components/flapper/behaviors/flapper_spinning_behavior_test.dart

@@ -36,10 +36,10 @@ void main() {
         'beginContact plays the flapper animation',
         (game) async {
           final behavior = FlapperSpinningBehavior();
-
           final entrance = FlapperEntrance();
           final flap = FlapSpriteAnimationComponent();
-          final flapper = Flapper.test(children: [entrance, flap]);
+          final flapper = Flapper.test();
+          await flapper.addAll([entrance, flap]);
           await entrance.add(behavior);
           await game.ensureAdd(flapper);