Implement Zarr v3 and sharding

[normanrz]

Detailed Description

Zarr v3 is now under consideration for approval. I think it is fine for us to now start implementing read support for it. There might be smaller changes down the road, but I don't expect major changes. Sharding is not as far in the approval process, but again I think we can start implementing.
The OME-NGFF spec is not yet prepared for Zarr v3, but I created a proposal that we could use preliminarily.

There is a sample dataset that we can use for testing (doesn't have the OME metadata yet): https://static.webknossos.org/data/zarr_v3/l4dense_motta_et_al_demo

[fm3]

@frcroth Also compare https://github.com/scalableminds/zarrita