Refactor Xenium + Visium paths and use better names

• all the paths used in notebooks 00_xenium_and_visium.ipynb, 01_xenium_and_visium.ipynb and 02_xenium_and_visium.ipynb should be placed in a config.py file
• sandbox.zarr was a poorly chosen name, rename it to manual_annotations.zarr. I have already made a copy in the S3 bucket of that file (so that now both sandbox.zarr.zip and manual_annotations.zarr.zip are present), so one needs just to adjust the notebooks.

00_xenium_and_visium.ipynb、01_xenium_and_visium.ipynb、02_xenium_and_visium.ipynb のパスから始め、次に config.py でそれらをどのように保持すべきか確認します。ノートブックを更新して sandbox.zarr の代わりに manual_annotations.zarr を使用し、すべてのパスが一元化され、名前変更された S3 コピーが参照されていることを確認します。