feat: disallowed adding components to a ComponentController

lib/flame/component_controller.dart

@@ -22,6 +22,11 @@ abstract class ComponentController<T extends Component> extends Component {
     );
     await super.addToParent(parent);
   }
+
+  @override
+  Future<void> add(Component component) {
+    throw Exception('ComponentController should not add other components.');
+  }
 }
 
 /// Mixin that attaches a single [ComponentController] to a [Component].

test/flame/component_controller_test.dart

@@ -31,6 +31,7 @@ void main() {
         );
       },
     );
+
     flameTester.test(
       'throws AssertionError when not attached to controlled component',
       (game) async {
@@ -44,6 +45,20 @@ void main() {
         );
       },
     );
+
+    flameTester.test(
+      'throws Exception when adding other component',
+      (game) async {
+        final component = ControlledComponent();
+        final controller = TestComponentController(component);
+
+        final anotherComponet = Component();
+        await expectLater(
+          () async => controller.add(anotherComponet),
+          throwsException,
+        );
+      },
+    );
   });
 
   group('Controls', () {