Replace Nose with an actively maintained unit testing library

[stennie]

Nose hasn't been maintained for years and has finally aged out of being compatible with Python 3.10

Choose your own adventure:

• https://wiki.python.org/moin/PythonTestingToolsTaxonomy
• pytest: https://docs.pytest.org (https://github.com/pytest-dev/nose2pytest)
• Nose2: https://docs.nose2.io/en/latest/differences.html
• Unittest: https://docs.python.org/3/library/unittest.html