test: add property tests for block and mask indexing

[maxrjones]

This is a complement to #4001 to improve property tests for block selection and mask selection.

These tests are left unmarked, so they run in the default test suite and the dedicated hypothesis.yaml CI job, matching the existing indexing hypothesis tests. I could make them as slow_hypothesis if we want to save ~10s on everyday test runs.

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

❌ Patch coverage is 86.95652% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.53%. Comparing base (b9d3964) to head (c206ed2).

Files with missing lines	Patch %	Lines
src/zarr/testing/strategies.py	86.95%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4054   +/-   ##
=======================================
  Coverage   93.53%   93.53%           
=======================================
  Files          88       88           
  Lines       11894    11917   +23     
=======================================
+ Hits        11125    11147   +22     
- Misses        769      770    +1     

Files with missing lines	Coverage Δ
src/zarr/testing/strategies.py	94.73% <86.95%> (+0.07%)	⬆️

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[dcherian]

Supporting rectilinear shouldn't be too hard to add? LGTM otherwise

[maxrjones]

Supporting rectilinear shouldn't be too hard to add? LGTM otherwise

good idea, I'll note that as a follow up