Describe the bug
When setting a node's parent via the parent property, the _isRoot flag of the child node is not updated to false. This omission causes an infinite loop when invoking parent.destroy(), as the child node incorrectly retains its _isRoot status, leading to circular references during destruction.

To Reproduce
Steps to reproduce the behavior:

  WebGLEngine.create({ canvas: 'canvas' })
  .then(engine => {
    engine.canvas.resizeByClientSize();

    const scene = engine.sceneManager.activeScene;
    const parent = scene.createRootEntity('parentEntity');
    const child = scene.createRootEntity('childEntity');

    parent.addChild(child);
    console.log('set parent by addChild, isRoot: ', child._isRoot);

    scene.addRootEntity(child);
    console.log('set root: ', child.parent, parent.children);

    child.parent = parent;
    console.log('set parent by set property, isRoot ', child._isRoot);

    scene.addRootEntity(child);
    console.log('set root: ', child.parent, parent.children);

    parent.destroy();

    engine.run();
  });

Expected behavior
The child node's _isRoot flag should automatically be set to false when assigned a parent.
parent.destroy() should clean up all child references without entering an infinite loop.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.