Add TetGen output capture and mesh quality warning system

[johannesring]

This PR adds basic parsing of TetGen’s terminal output in vmtkMeshGeneratorFsi to print warnings about potential mesh quality issues.

Some example thresholds (e.g. aspect ratio > 10) are used to trigger warnings, but these are not final — they’re just a starting point for discussion. No action is taken beyond logging.

Feedback on appropriate thresholds and how we should handle low-quality meshes is welcome.

Builds on the discussion in PR #219.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.29630% with 2 lines in your changes missing coverage. Please review.

Project coverage is 82.14%. Comparing base (6341898) to head (7de45d3).

Files with missing lines	Patch %	Lines
src/vasp/preprocessing/vmtkmeshgeneratorfsi.py	96.29%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #222      +/-   ##
==========================================
+ Coverage   82.00%   82.14%   +0.13%     
==========================================
  Files          32       32              
  Lines        4013     4065      +52     
==========================================
+ Hits         3291     3339      +48     
- Misses        722      726       +4     

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