refactor: make whitelist checks real-time

[ocetars]

Fixes: #4299
白名单检查策略改为 real-time
性能影响：每条消息多几次字典访问 + 一次列表推导式，都是内存操作，开销可忽略。

Modifications / 改动点

platform_settings = self._astrbot_config["platform_settings"]

• This is NOT a breaking change. / 这不是一个破坏性变更。

Screenshots or Test Results / 运行截图或测试结果

已按照 issue 方式验证通过

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Checklist / 检查清单

• 😊 如果 PR 中有新加入的功能，已经通过 Issue / 邮件等方式和作者讨论过。/ If there are new features added in the PR, I have discussed it with the authors through issues/emails, etc.
• 👀 我的更改经过了良好的测试，并已在上方提供了“验证步骤”和“运行截图”。/ My changes have been well-tested, and "Verification Steps" and "Screenshots" have been provided above.
• 🤓 我确保没有引入新依赖库，或者引入了新依赖库的同时将其添加到了 requirements.txt 和 pyproject.toml 文件相应位置。/ I have ensured that no new dependencies are introduced, OR if new dependencies are introduced, they have been added to the appropriate locations in requirements.txt and pyproject.toml.
• 😮 我的更改没有引入恶意代码。/ My changes do not introduce malicious code.

Summary by Sourcery

增强内容：

• 在白名单检查阶段存储对 Astrbot 配置的引用，并在每条消息上重新计算白名单和标志值，以确保行为始终保持最新。

Original summary in English

Summary by Sourcery

Enhancements:

• Store a reference to the Astrbot configuration in the whitelist check stage and derive whitelist and flag values on each message for up-to-date behavior.

[sourcery-ai]

嘿，我已经审查了你的更改，看起来很棒！

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Original comment in English

Hey - I've reviewed your changes and they look great!

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