(feat): support for zarr-python>=3.0.0b0

[ilan-gold]

• Closes Support zarr v3 #1817
• Tests added
• Release note added (or unnecessary)

[codecov]

Codecov Report

Attention: Patch coverage is 70.58824% with 25 lines in your changes missing coverage. Please review.

Project coverage is 82.20%. Comparing base (21d191d) to head (1687554).

Files with missing lines	Patch %	Lines
src/anndata/_io/specs/methods.py	63.88%	13 Missing ⚠️
src/anndata/_core/sparse_dataset.py	22.22%	7 Missing ⚠️
src/anndata/_settings.py	80.00%	2 Missing ⚠️
src/anndata/tests/helpers.py	71.42%	2 Missing ⚠️
src/anndata/_io/specs/registry.py	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1726      +/-   ##
==========================================
- Coverage   87.10%   82.20%   -4.90%     
==========================================
  Files          40       40              
  Lines        6135     6177      +42     
==========================================
- Hits         5344     5078     -266     
- Misses        791     1099     +308     

Files with missing lines	Coverage Δ
src/anndata/_io/utils.py	77.95% <ø> (ø)
src/anndata/_io/zarr.py	52.50% <100.00%> (-31.05%)	⬇️
src/anndata/compat/__init__.py	69.67% <100.00%> (-15.17%)	⬇️
src/anndata/experimental/merge.py	91.83% <100.00%> (+0.04%)	⬆️
src/anndata/_io/specs/registry.py	95.13% <92.30%> (-0.89%)	⬇️
src/anndata/_settings.py	88.67% <80.00%> (-5.44%)	⬇️
src/anndata/tests/helpers.py	81.27% <71.42%> (-12.92%)	⬇️
src/anndata/_core/sparse_dataset.py	90.18% <22.22%> (-3.57%)	⬇️
src/anndata/_io/specs/methods.py	85.07% <63.88%> (-3.54%)	⬇️

... and 8 files with indirect coverage changes

[ilan-gold]

blockers:

• v2 Object Encoding in 3.x.x python package zarr-developers/zarr-python#2500
• structured array encoding [v3] Structured dtype support zarr-developers/zarr-python#2134