1446 add api for guidance

[manuelgloeckler]

This adds an API for post-hoc modifications of the trained score estimator, allowing modifications of the likelihood or prior, the support, or other additional constraints. This addresses issue #1446 .

To does:

• Adds general API inline with current iid_method
• Refactor the parameterizations from stringly type to strongly typed (also for iid!)
• Adds some useful explanatory guidance approaches:
  • Classifier free guidance
  • Universal guidance - interval truncations.

[codecov]

Codecov Report

❌ Patch coverage is 67.21311% with 160 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.83%. Comparing base (937efc2) to head (672514b).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
sbi/utils/vector_field_utils.py	65.78%	103 Missing ⚠️
sbi/inference/potentials/vector_field_adaptor.py	68.18%	56 Missing ⚠️
sbi/inference/potentials/vector_field_potential.py	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1482      +/-   ##
==========================================
- Coverage   88.54%   83.83%   -4.72%     
==========================================
  Files         137      136       -1     
  Lines       11515    11797     +282     
==========================================
- Hits        10196     9890     -306     
- Misses       1319     1907     +588     

Flag	Coverage Δ
fast	83.83% <67.21%> (?)
full	?

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Files with missing lines	Coverage Δ
sbi/inference/posteriors/vector_field_posterior.py	69.12% <ø> (-8.06%)	⬇️
...i/neural_nets/estimators/flowmatching_estimator.py	81.66% <ø> (-15.00%)	⬇️
sbi/inference/potentials/vector_field_potential.py	75.20% <90.90%> (-15.87%)	⬇️
sbi/inference/potentials/vector_field_adaptor.py	78.19% <68.18%> (ø)
sbi/utils/vector_field_utils.py	66.12% <65.78%> (-17.21%)	⬇️

... and 25 files with indirect coverage changes