psense: fix facetting and add xlabel

[aloctavodia]

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📚 Documentation preview 📚: https://arviz-plots--123.org.readthedocs.build/en/123/

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 11.11111% with 8 lines in your changes missing coverage. Please review.

Project coverage is 81.18%. Comparing base (d35626b) to head (bc429a9).

Files with missing lines	Patch %	Lines
src/arviz_plots/plots/psensequantitiesplot.py	11.11%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #123      +/-   ##
==========================================
- Coverage   81.36%   81.18%   -0.19%     
==========================================
  Files          27       27              
  Lines        3156     3163       +7     
==========================================
  Hits         2568     2568              
- Misses        588      595       +7     

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