Support à la carte dependencies

scraperlib grew significantly over the years, with modules very useful even beyond pure scraper usages. The ZIM wrapper is very useful in itself to name only one.

We are also considering addition of the currently separate kiwixstorage module, or the Kiwix catalog reader.

To support this Kiwix Swiss-army knife layout, we'd need to be able to install only some of the dependencies.

Dependencies would thus be organized into extra groups (ZIM, image, video, etc) with an all group that installs everything of course.

In addition, we could maybe had a try block on imports in each module to print a user-actionable message when importing code for which dependencies are not installed.

まず、プロジェクトの依存関係設定と、issue で言及されているモジュールの import を確認します。all グループを含め、ZIM、image、video の extras をどのように整理するかを定義し、依存関係が不足している場合のメッセージを対象範囲に含めるかどうかを判断します。選択した extras を個別にインストールでき、合意した import の動作がカバーされれば完了です。