Refactor ppe

[aloctavodia]

This refactor ppe in preparation of further changes. I also implemented a "pathfinder" method. At this point, the main goal of that method is to help development and debugging of the "projective" method. But we may want to leave it as an option too.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 79.74684% with 16 lines in your changes missing coverage. Please review.

Project coverage is 81.54%. Comparing base (f25da81) to head (53d16ab).
Report is 39 commits behind head on main.

Files with missing lines	Patch %	Lines
preliz/predictive/ppe.py	60.00%	12 Missing ⚠️
preliz/ppls/pymc_io.py	86.66%	2 Missing ⚠️
preliz/ppls/bambi_io.py	80.00%	1 Missing ⚠️
preliz/predictive/ppa.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #579      +/-   ##
==========================================
- Coverage   82.23%   81.54%   -0.69%     
==========================================
  Files         101      109       +8     
  Lines        8020     8417     +397     
==========================================
+ Hits         6595     6864     +269     
- Misses       1425     1553     +128     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.