test(examples): test scripts instead of notebooks

[wpbonelli]

Testing example scripts directly instead of notebooks in CI makes it easier to see what the error message is when they fail. Also update deprecated pyvista syntax in vtk_pathlines_example.py

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.5%. Comparing base (7eb7c88) to head (88a0c09).
Report is 27 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2517      +/-   ##
===========================================
- Coverage     76.1%    55.5%   -20.7%     
===========================================
  Files          296      644     +348     
  Lines        64215   124227   +60012     
===========================================
+ Hits         48885    68971   +20086     
- Misses       15330    55256   +39926     

see 488 files with indirect coverage changes

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