Move files from Figshare to an alternative repo

[dbdimitrov]

Figshare links no longer work to obtain anndatas etc programatically. We should change to an alternative host repository.

See decoupler's / scverse standard: https://github.com/scverse/decoupler/blob/84d177d37a059ac043ea899e82d1ea7a1cfc8e14/src/decoupler/ds/_scell.py#L64

[Zethson]

If liana-py ever makes it to our scverse org, we can host the datasets on our scverse AWS S3.