prevote/vote中获取last_log_id()时，为什么需要去触发一下log flush呢，有什么考虑吗？是不是没有必要去做flush呢？

[node.cpp:1634](https://github.com/baidu/braft/blob/59c40e5d6b487121af5a1826a654138f489d7155/src/braft/node.cpp#L1634C5-L1634C63)
```
const LogId last_log_id = _log_manager->last_log_id(true);
```
_log_manager->last_log_id(true)传true的话会触发log flush

Start at node.cpp:1634 and trace LogManager::last_log_id(true) to understand why the flush is triggered during prevote/vote. Check the surrounding Raft durability assumptions and identify whether the intended outcome is to retain, remove, or document the flush; completion requires a maintainer decision because the issue does not define a concrete change or test.

Written by the indexing model from the issue text.