refactor workflow to install from build configuration and use pytest and tox

[zacharyburnett]

This PR refactors the workflow CI to run on push to master or on a pull request, and additionally uses tox to run lint / build checks before running tests with pytest-xdist.

blocked by #217:

AttributeError: module 'numpy' has no attribute 'int'. Did you mean: 'inf'?

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@d4e1c66). Click here to learn what that means.
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #218   +/-   ##
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  Coverage          ?   87.17%           
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  Files             ?       17           
  Lines             ?     1333           
  Branches          ?        0           
=========================================
  Hits              ?     1162           
  Misses            ?      171           
  Partials          ?        0           

Flag	Coverage Δ
unit	87.17% <0.00%> (?)

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[pllim]

This package is not my turf so I'll refrain from review. Feel free to ping me though for specific questions. Thanks!

[stscirij]

I dont have any experience with tox, and almost none with github actions, but it looks like the tests pass so looks good to me