TimerThread的run_and_delete中用了memory_order_relaxed内存序，是否会导致与unschedule的竞争问题

**Is your feature request related to a problem? (你需要的功能是否与某个问题有关?)**
在braft的代码中，依赖于bthread_timer_del返回0来释放一些变量的内存。但是我研究TimerThread觉得这里似乎不是100%安全的，如下图所示。

**Describe the solution you'd like (描述你期望的解决方法)**

用更安全的内存序
**Describe alternatives you've considered (描述你想到的折衷方案)**

**Additional context/screenshots (更多上下文/截图)**

Start by tracing TimerThread::run_and_delete, unschedule, and bthread_timer_del, focusing on the memory_order_relaxed operation shown in the issue. Review the concurrent paths and existing timer tests to determine whether unschedule can race with cleanup. Done means a justified memory-order change, or evidence that the current ordering is safe, with regression coverage.

Written by the indexing model from the issue text.