Handle scalar array and vars named c in ManifestStore

[maxrjones]

Improves the extraction of chunk indexes from the node name/key in the Zarr hierarchy to support scalar values and variables named c.

• Closes Generate a test case for ManifestStore with scalar arrays #530
• Closes ManifestStore fails to parse chunk indexes for array keys ending with the letter c. #671
• Closes Avoid loading scalar values automatically? #270
• Tests added
• Tests passing
• Full type hint coverage
• Changes are documented in docs/releases.rst
• New functions/methods are listed in api.rst
• New functionality has documentation

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.42%. Comparing base (8128451) to head (b9856a6).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #672      +/-   ##
===========================================
+ Coverage    88.37%   88.42%   +0.05%     
===========================================
  Files           33       33              
  Lines         1772     1780       +8     
===========================================
+ Hits          1566     1574       +8     
  Misses         206      206              

Files with missing lines	Coverage Δ
virtualizarr/manifests/manifest.py	88.11% <100.00%> (-0.09%)	⬇️
virtualizarr/manifests/store.py	88.46% <100.00%> (+0.18%)	⬆️
virtualizarr/manifests/utils.py	91.80% <100.00%> (+0.73%)	⬆️
virtualizarr/parsers/hdf/hdf.py	95.34% <100.00%> (+0.07%)	⬆️

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[maxrjones]

@TomNicholas @chuckwondo I'm not sure how to fix the type errors in https://github.com/zarr-developers/VirtualiZarr/actions/runs/16268967587/job/45931374285?pr=672. Do you have any suggestions?

[TomNicholas]

The sudden failures are caused by the release of zarr-python 3.10 today - see #676