[Bug]: 暗黑模式鸿蒙首次打开flutter页面初始获取暗黑模式不正确

### 请描述遇到的问题，以及您所期望的正确的结果

flutter_boost-4.6.5

大佬Help
DevEco Studio版本：DevEco Studio 5.0.5 Release SDK版本：5.1.0

flutter_boost-4.6.5

鸿蒙+flutterboost，
暗黑模式鸿蒙首次打开flutter页面闪一下白屏然后变黑，分析发现是flutter端 前400ms多次拿theme的model是默认的light， dark model延迟返回了半秒左右时间，导致白黑快速切换 出现闪一下。

复现的平台
鸿蒙

Flutter SDK版本
Flutter 3.7.12-ohos-1.1.1 • channel br_3.7.12-ohos-1.1.1 • https://gitcode.com/openharmony-tpc/flutter_flutter.git Framework • revision 1ef8f8d4ad (5 months ago) • 2025-06-03 17:07:07 +0800 Engine • revision 1a65d409c7 Tools • Dart 2.19.6 • DevTools 2.20.0

FlutterBoost版本 flutter_boost-4.6.5'

鸿蒙如何预热

Reproduce the first Flutter page opening on HarmonyOS with flutter_boost-4.6.5, Flutter 3.7.12-ohos-1.1.1, DevEco Studio 5.0.5, and SDK 5.1.0. Inspect the initial theme retrieval and the reported delayed dark-mode model; done means the first page opens without a white-to-dark flash and the required preheating behavior is documented or corrected.

Written by the indexing model from the issue text.