Update numcodecs tests and docs for zarr-python 3.0

[normanrz]

• Updates docs with new terms (e.g. compressors, filters, serializer)
• Overrides _Numcodecs.__repr__ because I was getting bulky names in zarr-python tests (e.g. _make_array_array_codec.<locals>._Codec(codec_name='numcodecs.delta', codec_config={'id': 'delta'})) although the code is setting __name__. Advice appreciated.
• Change tests to use zarr.create_array and zarr.open_array

TODO:

• Unit tests and/or doctests in docstrings
• Tests pass locally
• Docstrings and API docs for any new/modified user-facing classes and functions
• Changes documented in docs/release.rst
• Docs build locally
• GitHub Actions CI passes
• Test coverage to 100% (Codecov passes)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.92%. Comparing base (7cdffa1) to head (a2f4b9b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #675       +/-   ##
===========================================
+ Coverage   89.80%   99.92%   +10.12%     
===========================================
  Files          62       62               
  Lines        2747     2754        +7     
===========================================
+ Hits         2467     2752      +285     
+ Misses        280        2      -278     

Files with missing lines	Coverage Δ
numcodecs/tests/test_zarr3.py	100.00% <100.00%> (+94.73%)	⬆️
numcodecs/zarr3.py	100.00% <100.00%> (+94.47%)	⬆️

[dstansby]

Is this something it would be good to release before zarr-python 3.0? If so I can try and wrap up some other PRs, and do a 0.15 release.

[normanrz]

Is this something it would be good to release before zarr-python 3.0? If so I can try and wrap up some other PRs, and do a 0.15 release.

That would be nice but not required.