pyspy: sampler thread shutdown blocks until next sample

looks like this code
```
let sampler_output = sampler.take_while(|_x| running.load(Ordering::Relaxed));
```
blocks until the next sample (up to 10ms with default config)
We should consider exposing the channel so that we don't wait for 10ms

从 issue 中显示的 sampler.take_while 闭包开始，阅读 sampler 的关闭路径，重点关注 running 标志如何与等待下一个 sample 进行交互。确认默认等待时间为 10ms，然后验证停止 sampler 时能够完成，而无需不必要地等待另一个 sample。

由索引模型根据 Issue 内容生成。