Implement support for structured and struct zarr-extension defined dtypes

[BrianMichell]

Updates for consistency with the zarr-extension for structured types.

Implements legacy read-only for structured type and support for new struct definition.

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/user-guide/*.md
• Changes documented as a new file in changes/
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[d-v-b]

this looks great, thanks for this. Instead of modifying the existing structured data type, can we make struct as a subclass of that data type, and register it? That means people who need the legacy dtype can still use it (by overriding the registry)

[BrianMichell]

this looks great, thanks for this. Instead of modifying the existing structured data type, can we make struct as a subclass of that data type, and register it? That means people who need the legacy dtype can still use it (by overriding the registry)

Should be good to go now!

[BrianMichell]

@d-v-b Is there anything I can do to move this PR forward?

[codecov]

Codecov Report

❌ Patch coverage is 92.53731% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.89%. Comparing base (c966cfa) to head (1a6e371).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/zarr/codecs/bytes.py	60.00%	4 Missing ⚠️
src/zarr/core/dtype/npy/structured.py	98.18%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3781      +/-   ##
==========================================
- Coverage   92.98%   92.89%   -0.09%     
==========================================
  Files          87       87              
  Lines       11246    11309      +63     
==========================================
+ Hits        10457    10506      +49     
- Misses        789      803      +14     

Files with missing lines	Coverage Δ
src/zarr/core/array.py	97.64% <100.00%> (ø)
src/zarr/core/dtype/__init__.py	100.00% <100.00%> (ø)
src/zarr/dtype.py	100.00% <ø> (ø)
src/zarr/core/dtype/npy/structured.py	92.56% <98.18%> (-6.37%)	⬇️
src/zarr/codecs/bytes.py	92.75% <60.00%> (-5.58%)	⬇️

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[d-v-b]

@d-v-b Is there anything I can do to move this PR forward?

hi @BrianMichell thanks for the ping, I will get a review in soon. since numpy is handling the actual data type, I think we will ask much less of you than the tensorstore devs :)