Issue 290 - Add pip check

[csala]

Resolve #290

Add pip check commands to the local lint command to the GitHub Actions Unit Tests workflow, to make sure that the dependency ranges are all valid for all the OSs and Python versions.

Also slightly re-organize tox and the Github workflows to follow a standard pattern of running everything with invoke.

[amontanez24]

Changes looks good! Just had one question

[amontanez24]

Why does this one end in .[dev] when the others are pip install invoke .[test]?

[csala]

This one is installing the dev extras to include all the code style checks (flake8, isort...). The others can do with just the test dependencies, which is a smaller list.

[pvk-developer]

LGTM!
I only wonder why all the changes to python -m instead of just <entrypoint> command

[codecov-commenter]

Codecov Report

Merging #295 (37c0e2f) into v0.6.0-dev (eb4f5fa) will increase coverage by 0.12%.
The diff coverage is 78.33%.

@@              Coverage Diff               @@
##           v0.6.0-dev     #295      +/-   ##
==============================================
+ Coverage       81.69%   81.81%   +0.12%     
==============================================
  Files              10       11       +1     
  Lines             825      825              
==============================================
+ Hits              674      675       +1     
+ Misses            151      150       -1     

Impacted Files	Coverage Δ
rdt/transformers/base.py	46.07% <47.42%> (ø)
rdt/__init__.py	34.48% <50.00%> (ø)
rdt/transformers/boolean.py	86.48% <61.53%> (ø)
rdt/transformers/datetime.py	78.78% <67.85%> (-6.07%)	⬇️
rdt/transformers/numerical.py	76.76% <69.76%> (+3.00%)	⬆️
rdt/transformers/categorical.py	91.16% <86.66%> (+0.46%)	⬆️
rdt/transformers/addons/identity/identity.py	87.50% <87.50%> (ø)
rdt/transformers/null.py	96.15% <92.30%> (ø)
rdt/transformers/__init__.py	96.55% <96.00%> (-0.17%)	⬇️
rdt/hyper_transformer.py	100.00% <100.00%> (ø)
... and 9 more

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[csala]

LGTM! I only wonder why all the changes to python -m instead of just <entrypoint> command

The reason was just standardization: Some workflows used python -m pip while others called pip directly, so I chose one to make it uniform. And when choosing, I opted for the python -m syntax because it is the recommended one in the packaging docs, but to be honest I think that in this case plain pip would just work too.