Added pre-commit

[Markus28]

• This PR adds the checks that are defined in the Makefile as pre-commit hooks.
• Hopefully, the checks are equivalent to those from the Makefile, but I can't guarantee it.
• CI remains as it is.
• As I pointed out on discord, I experienced some conflicts between flake8 and yapf, so it might be better to transition to some other combination (e.g. black).

[Markus28]

Sorry, I ran the wrong python version. It appears mypy isn't happy on Python 3.7. I added the ignore hints back.

[Markus28]

I needed to add some new type: ignore because the mypy version changed for CI. This should also fix the CI for other PRs (e.g. the PettingZoo one). It might be a good idea to pin the mypy version.

[codecov-commenter]

Codecov Report

Merging #752 (5b70a5c) into master (65c4e3d) will decrease coverage by 1.11%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master     #752      +/-   ##
==========================================
- Coverage   90.53%   89.42%   -1.12%     
==========================================
  Files          70       70              
  Lines        4925     4925              
==========================================
- Hits         4459     4404      -55     
- Misses        466      521      +55     

Flag	Coverage Δ
unittests	89.42% <50.00%> (-1.12%)	⬇️

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

Impacted Files	Coverage Δ
tianshou/env/worker/subproc.py	57.29% <50.00%> (-29.73%)	⬇️

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[Trinkle23897]

I'd like to remove mypy in pre-commit because it has inconsistent behaviors with different python version and os, which will block contributors living in non py38+ubuntu2004

[nuance1979]

I support the transition from yapf to black. I personally find black more consistent with code formatting.

[Trinkle23897]

agree