Remove id from zarr3 config serialization

[normanrz]

Removes the "id" attribute from the serialization when used as zarr3 codec, because it is redundant.
Before

{"name": "numcodecs.zfpy", "configuration": {"id": "zfpy", "mode": 3, "precision": 20}}

After:

{"name": "numcodecs.zfpy", "configuration": {"mode": 3, "precision": 20}}

See https://ossci.zulipchat.com/#narrow/channel/423692-Zarr/topic/using.20numcodecs.20codecs.20with.20zarr_format.3D3/near/492599440

TODO:

• Unit tests and/or doctests in docstrings
• Tests pass locally
• 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 100.00%. Comparing base (5502dc8) to head (0236ca3).

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #685      +/-   ##
===========================================
+ Coverage   99.81%   100.00%   +0.18%     
===========================================
  Files          62        62              
  Lines        2752      2751       -1     
===========================================
+ Hits         2747      2751       +4     
+ Misses          5         0       -5     

Files with missing lines	Coverage Δ
numcodecs/json.py	100.00% <ø> (+3.92%)	⬆️
numcodecs/tests/test_zarr3.py	100.00% <100.00%> (+3.12%)	⬆️
numcodecs/zarr3.py	100.00% <100.00%> (ø)