Add `Cache::flexiable` support (#718)
* Adds `Cache::flexible` support
* Enhance composer.json files with suggested package requirements
* Enhance composer.json with additional suggested package for defer function
* 添加 `Cache::flexible` 方法以支持后台刷新过期缓存项
* 在 `Cache` 类中添加对 `flexible` 方法的 PHPStan 忽略注释
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Co-authored-by: Deeka Wong <8337659+huangdijia@users.noreply.github.com>