Update translators.kerchunk in preparation for TIFF reader fix

[elyall]

• 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

Two small changes:

1. virtual_vars_from_kerchunk_refs now takes in arr_refs instead of refs. This allows a single array to be wrapped.
2. find_groups is spun out. TIFFs can store a Dataset or a DataArray. So I was imagining this could be used for something like:

refs = kerchunk.tiff_to_zarr(urlpath)
is_dataarray = find_groups({"refs": refs}) == []

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.86%. Comparing base (5e66ad0) to head (05b4c41).
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #297      +/-   ##
==========================================
+ Coverage   80.16%   81.86%   +1.69%     
==========================================
  Files          41       41              
  Lines        2516     2553      +37     
==========================================
+ Hits         2017     2090      +73     
+ Misses        499      463      -36     

Flag	Coverage Δ
unittests	81.86% <100.00%> (+1.69%)	⬆️

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