Feature/build fixes

[Jammy2211]

Fixes to autofit as integration testing on build server raises issues:

• TruncatedGaussian added to registered prior type in __init__.
• Reinstate import of plot module at autofit level.
• Prevent samples without PDF from breaking latent variable sampler.
• Remove af.Gaussian as it is confusing with af.GausssianPrior, just use af.ex.Gaussian

Lots more integration tests still to go...

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.10%. Comparing base (ed0ab04) to head (416bf1a).
⚠️ Report is 17 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1158      +/-   ##
==========================================
- Coverage   80.16%   80.10%   -0.07%     
==========================================
  Files         206      207       +1     
  Lines       16010    16026      +16     
==========================================
+ Hits        12835    12837       +2     
- Misses       3175     3189      +14     

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