[功能请求]记忆上一次退出聊天的地方

### QQ(TIM) 版本 / QQ(TIM) Version

QQ9.1.15

### 为什么你认为需要此功能

大群聊内不漏信息，不用每次都必须吧所有信息看完，方便下次从离开的地方继续

### 联系到哪些已经存在的 bug 或者功能

_No response_

### 具体功能需要 / Detailed features requirements

记忆上一次退出聊天的位置，下次打开时自动跳转

Start by tracing how a chat is opened and how the current scroll or message position is represented in QAuxiliary. Identify where that position could be retained between exits, then verify that reopening the same chat returns to it without skipping newer messages.

Written by the indexing model from the issue text.