Added facade functions to_zarr and from_zarr

[pSpitzner]

Description

This adds to_zarr and from_zarr on the module level.

Before, prefixing by InferenceData was needed, now both of the following should work

import arviz as az
idata = az.InferenceData.from_zarr(my_store)
idata = az.from_zarr(my_store)

Checklist

• Follows official PR format
• New features are properly documented (with an example if appropriate)?
• Includes new or updated tests to cover the new feature
• Code style correct (follows pylint and black guidelines)
• Changes are listed in changelog

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📚 Documentation preview 📚: https://arviz--2236.org.readthedocs.build/en/2236/

[OriolAbril]

Thanks for the PR! I have added a couple comments, sorry I missed the PR

[codecov]

Codecov Report

Merging #2236 (c7f2227) into main (37540cd) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2236   +/-   ##
=======================================
  Coverage   87.89%   87.90%           
=======================================
  Files         121      122    +1     
  Lines       12448    12458   +10     
=======================================
+ Hits        10941    10951   +10     
  Misses       1507     1507           

Impacted Files	Coverage Δ
arviz/data/__init__.py	100.00% <100.00%> (ø)
arviz/data/io_zarr.py	100.00% <100.00%> (ø)

[pSpitzner]

Hi @OriolAbril,

thanks for putting in the fixes and merging!