Integrate Zarr v3 compatibility module with registry.

[sharkinsspatial]

Over in Virtualizarr we're in the process of transitioning our internal metadata model to Zarr v3 zarr-developers/VirtualiZarr#424 and in turn need to now update our codec pipeline specifications to v3 as well. Some of format readers extract codec configuration from archival files using format specific libraries (like h5py) and use that conf along with the numcodecs registry to return concrete Codec types.

Can we extend the registry to support returning Zarr v3 compatible codecs as well? I started exploring a PR but I was a bit unsure of how to tackle the optional Zarr v3 dep. I think the easiest path here might be separate zarrv3 registry module so that would raise the same ImportError. Any thoughts on the best path forward here?

[d-v-b]

codecs are only sensitive to the zarr v2 / zarr v3 distinction in their JSON representation. So if we can ensure that each codec can serialize to / from a zarr v2 or zarr v3 JSON representation, then there should be no problem with having the v3 codecs in the registry. And we 100% need to drop the zarr-python dependency.