feat!: Make columns non-nullable by default

[AndreasAlbertQC]

Motivation

Implements #20

Changes

• Changed the default of nullable from True to False
• Replaced FutureWarning
• Added a test for the skip_if decorator we otherwise don't use anymore right now. I expect we will use it again for future deprecations, so I figured it should stay in the code base.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (53c72bd) to head (40a2dcc).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #174   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           50        50           
  Lines         2904      2894   -10     
=========================================
- Hits          2904      2894   -10     

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[borchero]

Neat, just small questions related to the tests

[delsner]

Thanks, looks good modulo @borchero's questions.

[borchero]

Thanks for the explanation!