Migrate tests to nose2 instead of nose

[desilinguist]

• Update all tests to be nose2-compatible.
• Update pre-commit config to ignore docstyle and flake8 errors in test files.
• Replace nose with nose2 in requirements file.
• Update Gitlab and Azure CI builds to use nose2.
• Add unittest.cfg for nose2 configuration
• Move testing utilities into new skll.utils.testing module since nose2 doesn't pick up the tests directory as a module.
• Update all tests to use skll.utils.testing.
• Update .coveragerc with proper exclusions.
• Disable logging in very noisy test file.

This PR closes #746.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (9e501a9) 95.24% compared to head (3a28d57) 95.24%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #747   +/-   ##
=======================================
  Coverage   95.24%   95.24%           
=======================================
  Files          29       29           
  Lines        3578     3578           
=======================================
  Hits         3408     3408           
  Misses        170      170           

see 1 file with indirect coverage changes

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[mulhod]

There are still references to nosetests in CONTRIBUTING.md. Also it is said there that python=3.10 is required for setting up a development environment. Maybe that's still true for other reasons, but I think it should be considered. I actually set up an environment that uses 3.11 and I think the unit tests are running fine with nose2.

[desilinguist]

There are still references to nosetests in CONTRIBUTING.md. Also it is said there that python=3.10 is required for setting up a development environment. Maybe that's still true for other reasons, but I think it should be considered. I actually set up an environment that uses 3.11 and I think the unit tests are running fine with nose2.

Good catch on CONTRIBUTING.md. As for Python 3.11, there's a separate issue #744 for that which I will work on after this one is merged. As part of that, I will also be switching the Azure build to 3.11 from 3.9.

[mulhod]

All unit tests passed with 3.11.