chore: switch default plotting backend to viz interface

[moe-ad]

Follow up to #2881.

Summary of tasks done:

• ansys-tools-visualization-interface is now added to plotting/graphics targets and doc/test dependency groups. This effectively switches the default backend to the viz interface backend.
• Tests have been rearranged in a way that makes them pass, outside this new order, tests seg fault a ton.
• Docstring tests have been updated.
• A fix was applied to _VisualizationInterfacePlotter.add_point_labels.
• Documentation updates made in doc/conf.py(as a workaround for labels not being captured for 03-labels.py example during CI documentation build).
• Updates made in doc/sphinx_gallery_examples/06-plotting/07-plot_on_geometries.py to improve visibility of elements on the plot.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.19%. Comparing base (30c2026) to head (37fe896).
⚠️ Report is 89 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3023      +/-   ##
==========================================
+ Coverage   82.62%   83.19%   +0.56%     
==========================================
  Files          92       92              
  Lines       11223    11227       +4     
==========================================
+ Hits         9273     9340      +67     
+ Misses       1950     1887      -63     

[github-actions]

The documentation for this pull request will be available at https://dpf.docs.pyansys.com/pull/3023. Please allow some time for the documentation to be deployed.

[github-actions]

This PR has been closed. Documentation for this pull request will shortly be removed from its former deployment address.