fix: reject a string-valued zero scale in the scale_offset codec

[dylanpulver]

Summary

ScaleOffset.validate compared self.scale against 0 before parsing it. scale is documented and typed as int | float | str, and no Python string equals 0, so "0" and "0.0" walked past the guard, as did the spec's hex form "0x0000000000000000".

On float dtypes the array is created, every chunk is written as zero and read back as NaN with no error. The zero scale is persisted into zarr.json, so reopening the store reproduces it. On integer dtypes it surfaces as an unhandled ZeroDivisionError instead of the ValueError the guard promises.

The comparison now runs on the value returned by from_json_scalar. That reorders one thing: given a bad offset and a zero scale together, the representability error fires first. Nothing asserted the old order.

Narrowing the annotation to drop str would also close it, but a string scale is a documented input and the suite already exercises offset="NaN".

Residual: scale="NaN" and scale=float("inf") are still accepted on float dtypes and also produce unusable reads. That reaches purely numeric input as well, so it reads as a separate question.

For reviewers

The reorder is the only behavior change beyond the new rejection. test_rejects_zero_scale is now parametrized; the three string cases fail on main and pass here, and the two numeric cases pass either way.

Full suite: 6908 passed, 461 skipped, 4 xfailed. ruff 0.16.0 check and format clean. mypy 2.3.0 clean.

Author attestation

• I am a human, these are my changes, and I have reviewed and understood every change and can explain why each is correct.

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)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.12%. Comparing base (bf8f863) to head (749e970).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4279   +/-   ##
=======================================
  Coverage   94.12%   94.12%           
=======================================
  Files          92       92           
  Lines       12830    12831    +1     
=======================================
+ Hits        12076    12077    +1     
  Misses        754      754           

Files with missing lines	Coverage Δ
src/zarr/codecs/scale_offset.py	100.00% <100.00%> (ø)

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[d-v-b]

looks good, thanks for the fix and sorry about the bug