the future of `zarr.codecs.numcodecs`

[d-v-b]

Now Zarr has a copy of all the codecs from numcodecs.zarr3, it makes sense to think about the future direction of those codecs.

The design of these codecs was chosen for development speed, not user-friendliness or ergonomics (I'm happy to give examples here but I think browsing the source code conveys my point quickly enough. So I think we should move to implement complete implementations of each of these codecs in this library, and deprecate the old hastily created ones.