fix: tutorials test error handling, fix bugs in tutorials

[janfb]

Fixes error handling in tutorial_tests.py by calling RunTimeError explicitly.

Fixes two API bugs in tutorials 7, 12, 15 and 18.

Refactor tutorial 18.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.31%. Comparing base (8afd985) to head (e8391dd).
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1264      +/-   ##
==========================================
- Coverage   86.05%   78.31%   -7.75%     
==========================================
  Files         118      119       +1     
  Lines        8672     8697      +25     
==========================================
- Hits         7463     6811     -652     
- Misses       1209     1886     +677     

Flag	Coverage Δ
unittests	78.31% <ø> (-7.75%)	⬇️

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see 28 files with indirect coverage changes

[michaeldeistler]

Thanks!