[WIP] Update tp.el to preserve external properties during text updates

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

你是一个有20年经验的软件开发者和emacs专家，请完成下面的优化:For complete functionality, tp.el also needs to be updated to preserve external properties (like keymap, mouse-face, cursor) during reactive text updates. A companion PR should be submitted to the tp.el repository.

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