fix(miniapp-runtime): enter same page twice then exit should not throw error

[XGHeaven]

小程序先进入同一个页面两次，然后退出，此时触发生命周期事件会报错。
主要由两个原因：

• 页面的 id 使用的是路径，会导致同一个页面打开多次的时候冲突，从而让上一个页面退出后把后一个页面的事件存储实例也清除了。解决方式就是给 id 添加一个时间戳，保证每个页面的唯一性
• 在触发生命周期的方法中，没有正确判断为空的情况。解决方法是判空

[Copilot]

Pull Request Overview

This PR fixes an error when entering the same miniapp page twice and then exiting by ensuring each page has a unique id and guarding against null lifecycle events.

• Updated unique id generation in common.ts by appending a timestamp to guarantee uniqueness.
• Refactored hooks.ts to use React's useRef for consistent page instance management during lifecycle events.
• Added a changeset entry to document the patch.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/miniapp-runtime/src/dsl/common.ts	Appended a timestamp to options for generating a unique page id.
packages/miniapp-runtime/src/app/hooks.ts	Refactored instance retrieval using a useRef to better manage page lifecycle events.
.changeset/six-zebras-sniff.md	Added changeset metadata to record the patch.

Comments suppressed due to low confidence (2)

packages/miniapp-runtime/src/dsl/common.ts:133

• [nitpick] Consider adding a comment to explain the purpose of introducing '$iceTimestamp' to assist future maintainers and update any related tests if needed.

const uniqueOptions = Object.assign({}, options, { $iceTimestamp: Date.now() });

packages/miniapp-runtime/src/app/hooks.ts:22

• [nitpick] Adding a brief comment on the use of 'instRef' for storing the page instance can improve clarity during cleanup in the lifecycle hook.

let inst = instRef.current = getPageInstance(id);