Replace pytest.mark with pytask.mark.

[tobiasraabe]

Before this PR, pytask.mark was essentially pytest.mark. This PR implements the required logic.

It also adds a new hook for the main pytask call. This allows to short-circuit the pytask call on the command line to, e.g., print only all configured marks. Use pytask --markers to print all configured markers.

If you use a marker which has not been configured, an warning is printed.

[codecov]

Codecov Report

Merging #12 into main will decrease coverage by 5.17%.
The diff coverage is 94.92%.

@@            Coverage Diff             @@
##             main      #12      +/-   ##
==========================================
- Coverage   94.09%   88.92%   -5.18%     
==========================================
  Files          31       36       +5     
  Lines        1405     1769     +364     
==========================================
+ Hits         1322     1573     +251     
- Misses         83      196     +113     

Flag	Coverage Δ
#end_to_end	78.46% <86.95%> (-3.46%)	⬇️
#integration	49.80% <58.33%> (-1.31%)	⬇️
#unit	73.65% <71.73%> (-5.14%)	⬇️

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Impacted Files	Coverage Δ
src/pytask/mark/__init__.py	20.58% <ø> (ø)
tests/test_debugging.py	95.91% <0.00%> (ø)
src/pytask/cli.py	88.88% <75.00%> (-1.44%)	⬇️
src/pytask/mark/structures.py	88.76% <88.76%> (ø)
tests/test_mark.py	97.50% <97.50%> (ø)
src/pytask/__init__.py	100.00% <100.00%> (ø)
src/pytask/collect.py	91.59% <100.00%> (ø)
src/pytask/config.py	100.00% <100.00%> (+10.00%)	⬆️
src/pytask/execute.py	96.46% <100.00%> (ø)
src/pytask/hookspecs.py	100.00% <100.00%> (ø)
... and 22 more

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