Vendor kerchunk fits reader

[TomNicholas]

Passes locally with zarr v2. But I think this will break for an env with zarr v3 in it.

• Closes part of Vendor kerchunk readers? #377
• 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

Attention: Patch coverage is 0% with 123 lines in your changes missing coverage. Please review.

Project coverage is 71.23%. Comparing base (95fce11) to head (2433570).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
virtualizarr/vendor/kerchunk/fits.py	0.00%	83 Missing ⚠️
virtualizarr/vendor/kerchunk/codecs.py	0.00%	40 Missing ⚠️

❌ Your patch status has failed because the patch coverage (0.00%) is below the target coverage (75.00%). You can increase the patch coverage or adjust the target coverage.
❌ Your project status has failed because the head coverage (71.23%) is below the target coverage (75.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #399      +/-   ##
==========================================
- Coverage   75.62%   71.23%   -4.40%     
==========================================
  Files          33       35       +2     
  Lines        1994     2117     +123     
==========================================
  Hits         1508     1508              
- Misses        486      609     +123     

Files with missing lines	Coverage Δ
virtualizarr/vendor/kerchunk/codecs.py	0.00% <0.00%> (ø)
virtualizarr/vendor/kerchunk/fits.py	0.00% <0.00%> (ø)

[TomNicholas]

Note that in the kerchunk compatibility PR the FITS reader has now been updated to work with zarr-python v3. So we could just copy those changes here temporarily.

[maxrjones]

superseded by #406