Parametrize tests of Debye_length

[namurphy]

PlasmaPy's tests of Debye_length are currently consolidated into a single test function with multiple assert statements. This PR changes the test setup to use @pytest.mark.parametrize.

I've been meaning to get to this for a couple of years, but better late than never!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.36%. Comparing base (20e60aa) to head (17df492).
Report is 56 commits behind head on main.

❗ Current head 17df492 differs from pull request most recent head 64c2b5f. Consider uploading reports for the commit 64c2b5f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2509      +/-   ##
==========================================
+ Coverage   96.93%   97.36%   +0.43%     
==========================================
  Files         104      104              
  Lines        9163     9375     +212     
==========================================
+ Hits         8882     9128     +246     
+ Misses        281      247      -34     

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[ejohnson-96]

👍