pre-commit setup & code changes

[st--]

Separated out from #233

[codecov-commenter]

Codecov Report

Merging #241 (0470ffa) into v0.6 (75f9ddd) will decrease coverage by 0.19%.
The diff coverage is 97.28%.

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@@            Coverage Diff             @@
##             v0.6     #241      +/-   ##
==========================================
- Coverage   88.74%   88.55%   -0.19%     
==========================================
  Files          52       52              
  Lines        2016     1984      -32     
  Branches      179      175       -4     
==========================================
- Hits         1789     1757      -32     
  Misses        117      117              
  Partials      110      110              

Flag	Coverage Δ
unittests	88.55% <97.28%> (-0.19%)	⬇️

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

Impacted Files	Coverage Δ
gpjax/progress_bar.py	0.00% <0.00%> (ø)
gpjax/dataset.py	84.09% <50.00%> (-0.36%)	⬇️
gpjax/fit.py	79.01% <81.81%> (-0.51%)	⬇️
gpjax/__init__.py	100.00% <100.00%> (ø)
gpjax/base/__init__.py	100.00% <100.00%> (ø)
gpjax/base/module.py	80.46% <100.00%> (ø)
gpjax/base/param.py	100.00% <100.00%> (ø)
gpjax/gaussian_distribution.py	80.89% <100.00%> (-0.22%)	⬇️
gpjax/gps.py	95.48% <100.00%> (ø)
gpjax/kernels/__init__.py	100.00% <100.00%> (ø)
... and 38 more