Integrate KiwixStorage

Ours scrapers all depend on S3 and use KiwixStorage for it. That wrapper and repo are mostly untouched (yet working) and would great benefit from being integrated into scraperlib: tests, usage, dependencies update, better API, etc.

Now that we had experience using it, it probably make sense to reduce its API to what's actually used.

It's true that some non-scraper projects are using it (cardshop and zimfarm to upload to S3), but those are also using scraperlib and we've discussed making scraperlib's dependencies more modular via extras anyway.

まず、scraperlib とその scraper が現在 S3 と KiwixStorage をどのように使用しているかを確認し、その使用方法を python-storagelib API と比較します。要求されたテストと統合の追加、依存関係の更新、issue で説明されているより小さな API とモジュール型の依存関係構造の定義が完了すれば、作業完了です。