move build system to pyproject.toml

[larsbuntemeyer]

remove obsolete setup.py and setup.cfg, update pyproject.toml.

[codecov]

Codecov Report

Merging #209 (d2f25d1) into main (ee74fb1) will decrease coverage by 5.42%.
The diff coverage is 33.33%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #209      +/-   ##
==========================================
- Coverage   76.24%   70.83%   -5.42%     
==========================================
  Files          22       25       +3     
  Lines        1322     1423     +101     
==========================================
  Hits         1008     1008              
- Misses        314      415     +101     

Flag	Coverage Δ
unittests	70.83% <33.33%> (-5.42%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
cordex/preprocessing/preprocessing.py	62.61% <100.00%> (ø)
cordex/regions/_germany.py	100.00% <100.00%> (ø)
cordex/tables/_resources.py	73.17% <100.00%> (ø)
cordex/cmor/utils.py	91.12% <0.00%> (ø)
cordex/cmor/cmor.py	66.07% <37.50%> (ø)
cordex/esgf_access.py	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes