Convert tests/unit/fileformats/cf mesh content to PyTest

[trexfeathers]

The other content in the directory has already been converted.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.95%. Comparing base (e4caaee) to head (76833f8).
⚠️ Report is 109 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6633   +/-   ##
=======================================
  Coverage   89.95%   89.95%           
=======================================
  Files          91       91           
  Lines       24447    24447           
  Branches     4567     4567           
=======================================
  Hits        21992    21992           
  Misses       1686     1686           
  Partials      769      769           

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[ESadek-MO]

Please could you:

• correct the mock calls in test_CFReader and test_CFGroup
• remove the commented code in test_CFReader (line 370. _setup)

Feel free to veto if I'm pushing further out of scope.

[trexfeathers]

Please could you:

• correct the mock calls in test_CFReader and test_CFGroup
• remove the commented code in test_CFReader (line 370. _setup)

Feel free to veto if I'm pushing further out of scope.

Veto please. You're re-reviewing work that has already been approved as part of the conversion project: #5873

[ESadek-MO]

Happy with your changes, I'll add the others to #6625