Add Github Action to Run Pytest for push/pull-request Actions

[engineerjoe440]

Changes:

• Add .github/workflows/pytest.yml to define the installation of dependencies and execution of pytest to validate behavior.

Closing thoughts:

I'm loving what you've got here in this project, and I want to use it in some of my work, but to do that, I need to enhance a few things. Before I start with too much of that, I wanted to bring in some automated testing to validate changes I make, and prove them out so that you're at least somewhat confident that my changes won't destroy your work.

[engineerjoe440]

Thanks for being willing to allow contributions! If you're willing, I might add a few more CI plans for flake8 (since you pointed it out in the other PR I have open), and anything else I can! :)

[klauer]

Sure - that'd be great!

Just a thought, but you might consider just having pre-commit do the heavy lifting in CI (e.g., pre-commit run --all-files) instead of piece-meal flake8, isort --check-only, etc.