Support Zarr v3 format

[tomwhite]

In #288 we allowed bio2zarr to use zarr-python v2 or v3, while using the Zarr v2 format in both cases. This issue is to support using the v3 format.

I have written a draft of what changes are needed in VCF Zarr in sgkit-dev/vcf-zarr-spec#42.

The main changes that affect bio2zarr are:

• String types are encoded differently (this may also interact with NumPy 2's new StringDType).
• Dimension names are no longer written as a special _ARRAY_DIMENSIONS attribute, but are stored in the Zarr metadata as dimension_names.
• Zarr filters and compressors have been replaced with codecs.
• The directory layout has changed with chunks now being stored under a c prefix. This would affect some low-level bio2zarr code e.g.

  bio2zarr/bio2zarr/vcz.py

  Line 981 in 3f955ce

  # This is Zarr v2 specific. Chunks in v3 with start with "c" prefix.