Support member functions that are immediately implemented when declared

[N-Wouda]

This PR:

• Closes #xxxx.
• Adds and passes relevant tests.
• Has well-formatted code and documentation.

Details

Notes:

• It is essential that you add a test when making code changes.
  This keeps the code coverage level up, and helps ensure the changes work as intended.
• When fixing a bug, you must add a test that would produce the bug in the master branch, and then show that it is fixed with the new code.
• New code additions must be well formatted. Changes should pass the pre-commit workflow, which you can set up locally using pre-commit.
• Docstring additions must render correctly, including escapes and LaTeX.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b686388) to head (8ee832e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main        #9   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines           66        67    +1     
=========================================
+ Hits            66        67    +1     

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