Is there a method to check whether a file exists in the cache using its url?

## 💬 Questions and Help

Hi,

I've looked through the documentation, the issues on GitHub and source code.
I'd like to know, using its URL, if a file exists in the cache.

I've only found a private method in the cache manager's `CacheStore`: `_fileExists()`.
But since it's private, I cannot use it.

Any other suggestions?

Issue 将 CacheStore._fileExists() 指定为现有的私有入口点；首先阅读该方法以及周围的 cache-manager API 和文档。确定是否已经公开了基于 URL 的缓存存在性检查，然后在决定哪项更改或文档能够给出明确答案之前，先明确预期的公共行为。

由索引模型根据 Issue 内容生成。