不允许在方法内部创建线程池

## Rule content
.【强制】线程资源必须通过线程池提供，不允许在应用中自行显式创建线程，不允许在方法内部创建线程池。

## Problem description
在方法内部创建线程池等同于在应用中自行创建线程，在并发情况下，有可能造成系统创建大量同类线程面导致消耗内存或者“过度切换”的问题，也容易出现线程池不正确shutdown。

## Advice

The issue names no source file, test, or entry point. Start by locating the rule that checks thread creation and its existing tests, then verify how method-local thread-pool creation is represented. Done means the prohibited pattern is detected without permitting application-managed thread pools outside methods, with regression coverage.

Written by the indexing model from the issue text.