chore: add rectilinear hypothesis block indexing tests

[maxrjones]

Follow up on the comment from #4054 (review)

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 93.50%. Comparing base (bba0d0f) to head (92d4f51).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4075      +/-   ##
==========================================
+ Coverage   93.47%   93.50%   +0.02%     
==========================================
  Files          90       90              
  Lines       11958    11979      +21     
==========================================
+ Hits        11178    11201      +23     
+ Misses        780      778       -2     

Files with missing lines	Coverage Δ
src/zarr/testing/strategies.py	95.39% <100.00%> (+0.97%)	⬆️

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