nose -> pytest

[pyrox0]

With your PR, here is a check list:

• Has test cases written?
• Has all code lines tested?
• Has make format been run?
• Please update CHANGELOG.yml(not CHANGELOG.rst)
• Has fair amount of documentation if your change is complex
• Agree on NEW BSD License for your contribution

This moves the project from the unmaintained nose test runner to pytest, which is a standard python test runner these days. The tests are equivalent and all pass, same as before, and coverage is still measured. Note that the codecov action included in the workflow right now does not function, as per codecov docs the @v1 tag of codecov-action no longer functions.