SpringMVC异步情况下System的Thread限流计数有问题

## 背景
使用SpringMVC进行Sentinel限流，配置了System的Thread最大数限流规则。

当使用SpringMVC `@Callable` 异步模式后，SystemRule的当前线程数会不停的放大，一直递增不扣减，请求次数超过最大线程数就会出现BlockingException，后面所有请求都会是这个错，无法恢复。

业务代码：
```
@ResponseBody
@GetMapping("/async")
public Callable async() throws Exception {
Callable callable = () -> {
TimeUnit.MILLISECONDS.sleep(50); //
return "hello world";
};
return callable;
}
```

## 问题分析
通过打断点分析发现是因为SpringMVC异步情况下preHandle会进来两次，Sentinel的AbstractSentinelInterceptor拦截器会两次计数，导致Entry没有退出。

Start by tracing SpringMVC's @Callable async lifecycle through AbstractSentinelInterceptor, especially the repeated preHandle calls and SystemRule thread counting. Reproduce the issue with the provided /async endpoint, then verify that the count is released correctly and subsequent requests do not remain blocked by BlockingException.

Written by the indexing model from the issue text.