Replacing pytest -n auto with pytest -n %{_smp_build_ncpus}

[Miro Hrončok]

Hello Pythonistats, packagers,

A handful of Fedora Python packages uses pytest-xdist to run tests in parallel 
like this:

%pytest -n auto

-n auto means pytest will spawn a number of workers processes equal to the 
number of available CPUs.

In the spirit of other packaging guidelines, I believe we should use this instead:

%pytest -n %{_smp_build_ncpus}

This means the same thing in most of the ceases, but will limit the number of 
workers depending on other constraints in the spec or in the environment.

Should I do this in a mass change? Not so many packages use pytest -n auto in 
the spec:

$ rg -l -- '(-n|--numprocesses)(\s*|=)auto(\s|$)'
   ansible-bender.spec
   azure-cli.spec
   ocrmypdf.spec
   python-cartopy.spec
   python-GridDataFormats.spec
   python-hypothesis.spec
   python-matplotlib.spec
   python-mplcairo.spec
   python-rpmautospec.spec
   python-sqlalchemy.spec
   python-tox.spec
   python-xarray.spec
   python-zstandard.spec
   pythran.spec
   scipy.spec

(Other packages have that in tox.ini or pytest config file, but I am not aiming 
at changing that here.)

And, considering many other packages might want to benefit from that, should 
this be:

1) encouraged in the Python packaging guidelines
  2) macronized (I was thinking %pytest_parallel, but TBD)

?