refactor core codebase for code quality (this also changes signatures of some public functions)

[mbdevpl]

No description provided.

[jenkins-mbdev]

Tools report for GitHub-mbdevpl/argunparse/PR-7 [build #2]:

• Pylint: ran 🆗

• Mypy: ran 🆗

• Flake518: ran 🆗

• Pydocstyle: ran 🆗

• Coverage: 100% 🆗 (click for details)

  Name                              Stmts   Miss Branch BrPart  Cover   Missing
  -----------------------------------------------------------------------------
  argunparse/__init__.py                2      0      0      0   100%
  argunparse/_version.py                2      0      0      0   100%
  argunparse/argument_unparser.py      76      0     20      0   100%
  setup.py                              9      0      2      0   100%
  test/__init__.py                      6      0      0      0   100%
  test/examples.py                     12      0      0      0   100%
  test/test_argument_unparser.py      102      0     20      0   100%
  test/test_packaging.py                3      0      0      0   100%
  -----------------------------------------------------------------------------
  TOTAL                               212      0     42      0   100%
  

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.0%. Comparing base (9ea57d1) to head (09fc809).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main       #7   +/-   ##
=======================================
  Coverage   100.0%   100.0%           
=======================================
  Files           8        8           
  Lines         227      212   -15     
  Branches       32       21   -11     
=======================================
- Hits          227      212   -15     

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