Add all dependencies explicitly for intersphinx linking

[TomNicholas]

Also might as well add all your dependencies. You should add all dependencies even optional ones IMO

• numcodecs: https://numcodecs.readthedocs.io/en/stable/objects.inv
• fsspec: https://filesystem-spec.readthedocs.io/en/latest/objects.inv
• requests: https://requests.readthedocs.io/en/latest/objects.inv
• aiohttp: https://docs.aiohttp.org/en/stable/objects.inv
• s3fs: https://s3fs.readthedocs.io/en/latest/objects.inv
• h5py: https://docs.h5py.org/en/stable/objects.inv

I didn't go through the whole list of optional dependencies but you get the picture.

At least with mkdocs, it's important to add all of these intersphinx linkings so that all types get automatically linked. E.g. here where RecordBatch automatically links to the arro3 docs

Originally posted by @kylebarron in https://github.com/zarr-developers/VirtualiZarr/pull/503#discussion_r2010902203