Add S3 based optimization cache support

We use kiwix_storagelib for implementing S3 based optimization cache in the scrapers. However, this gives rise to redundant code. We put a version of the file along with the optimizer version as the metadata always. So, this can be better implemented in scraperlib. For a start, we can have a caching module that can have 3 functions, (or maybe a class containing methods). The primary 3 things we need are -

• download_from_cache()
• upload_to_cache()
• check_credentials()

There can be several ways to have this, but it should at least fulfill the following -

• Compare optimizer_version
• Compare file_version

Optional things can be to check file upload date and discard if it's older than a specified amount of time. If we go for a class based approach, we can also explore possibilities to improve performance.

首先检查 scrapers 中现有的 kiwix_storagelib 使用方式，以及 optimizer 和文件版本如何作为元数据存储。定义缓存入口点，并验证凭据、下载、上传以及两种版本比较都已覆盖；issue 中未指定具体文件或测试。