feat: migrate to zarr v3 defaults

[ilan-gold]

• Closes Flip zarr v3 settings to turned on  #2239
• Tests added

• Release note not necessary because:

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.68%. Comparing base (a7ba562) to head (993e477).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2439      +/-   ##
==========================================
- Coverage   85.69%   85.68%   -0.01%     
==========================================
  Files          49       49              
  Lines        7793     7791       -2     
==========================================
- Hits         6678     6676       -2     
  Misses       1115     1115              

Files with missing lines	Coverage Δ
src/anndata/_io/specs/methods.py	91.51% <100.00%> (-0.03%)	⬇️
src/anndata/_io/specs/registry.py	94.85% <ø> (ø)
src/anndata/_settings.py	92.59% <ø> (ø)

[flying-sheep]

this should make this not appear in the docs

Suggested change

	>>> adata.layers["dense"] = ad.experimental.read_elem_lazy(g["layers/dense"])
	>>> adata.layers["dense"]
	dask.array<from-zarr, shape=(2700, 32738), dtype=float32, chunksize=(169, 2047), chunktype=numpy.ndarray>
	>>> # TODO: remove ... once https://github.com/zarr-developers/zarr-python/issues/3602 becomes minimum zarr (3.1.6)
	..
	TODO: remove “...” once https://github.com/zarr-developers/zarr-python/issues/3602 becomes minimum zarr (3.1.6)
	>>> adata.layers["dense"] = ad.experimental.read_elem_lazy(g["layers/dense"])

[ilan-gold]

Ah, good to know - I thought # doesn't appear in docs based on https://docs.python.org/3/library/doctest.html#how-are-docstring-examples-recognized but I guess the rendering and the output/running are different, thanks.