Handle zipped zarr, where zarr is not visible in file path

[konstntokas]

Closes #4

Testing will be added in the next PR when I refactor the code to the new xcube's preload API.

[codecov]

Codecov Report

Attention: Patch coverage is 15.78947% with 16 lines in your changes missing coverage. Please review.

Project coverage is 40.49%. Comparing base (2eb6f4f) to head (2e526ab).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
xcube_zenodo/preload.py	9.09%	10 Missing ⚠️
xcube_zenodo/_utils.py	25.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #9      +/-   ##
==========================================
- Coverage   41.21%   40.49%   -0.73%     
==========================================
  Files           7        7              
  Lines         313      326      +13     
==========================================
+ Hits          129      132       +3     
- Misses        184      194      +10     

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