Added scalar coords of input cubes to output of esmpy_regrid

[schlunma]

Description

This PR adds missing scalar coordinates of the input cubes to the output of esmpy_regrid and fixes a bunch of Codacy issues in the corresponding files.

Closes #1810

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[codecov]

Codecov Report

Merging #1811 (3b42636) into main (a6f8c08) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1811      +/-   ##
==========================================
- Coverage   91.51%   91.49%   -0.02%     
==========================================
  Files         202      202              
  Lines       10908    10910       +2     
==========================================
  Hits         9982     9982              
- Misses        926      928       +2     

Impacted Files	Coverage Δ
esmvalcore/preprocessor/_regrid.py	97.11% <100.00%> (ø)
esmvalcore/preprocessor/_regrid_esmpy.py	89.88% <100.00%> (+0.11%)	⬆️
esmvalcore/cmor/check.py	97.38% <0.00%> (-0.38%)	⬇️

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[schlunma]

@zklaus would you be able to have a quick look at that? This is blocking me from #1808. Thanks 👍

[valeriupredoi]

looks good to me, cheeers, Manu! Just a bit of a nicer handling of an empty array/tuple

[sloosvel]

Nice!