Improve play mode test detection by preventing RuntimeInitializeOnLoadMethod registration

The previous fix checked TestRunnerCallbacks.IsRunningTests at runtime, but there was a
timing issue - RuntimeInitializeOnLoadMethod executes before TestRunnerCallbacks.RunStarted
is called, so the flag was not set yet.

This commit uses the cleaner approach recommended by Unity: prevent the method from being
registered at all during tests by applying #if !UNITY_INCLUDE_TESTS to the attribute itself.

This eliminates the runtime check and TestRunnerCallbacks dependency entirely from
ChangeScene.cs, making the code simpler and more reliable.

References:
- Unity Discussions: RuntimeInitializeOnLoadMethod runs during playmode unit tests
  https://discussions.unity.com/t/methods-with-runtimeinitializeonloadmethod-attribute-run-during-playmode-unit-tests/949876

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: JasonXuDeveloper

UnityProject/Packages/com.jasonxudeveloper.jengine.core/Editor/Misc/ChangeScene.cs

@@ -9,17 +9,12 @@ namespace JEngine.Core.Editor.Misc
     /// </summary>
     internal static class ChangeScene
     {
+        // Don't auto-change scenes during Play Mode tests
+#if !UNITY_INCLUDE_TESTS
         [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSceneLoad)]
+#endif
         private static void DoChange()
         {
-#if UNITY_INCLUDE_TESTS
-            // Skip scene change when running Play Mode tests
-            if (TestRunnerCallbacks.IsRunningTests)
-            {
-                return;
-            }
-#endif
-
             var jump = Settings.Instance.jumpStartUp;
             if (!jump) return;
             var scene = SceneManager.GetActiveScene();