Allow more distributions to be truncated

[ricardoV94]

Description

AS reported in https://discourse.pymc.io/t/custom-distribution-for-truncated-gamma/11006/7?u=ricardov94 SymbolicRandomVariable distributions like ExGaussian couldn't be Truncated. The reason why this restriction was inplace are technical, and have to do with not all SymbolicRandomVariables being completely encapsulated in the inner graph. For distributions like Mixture this would be quite some work (which we may still want to do).

However many SymbolicRandomVariables are fine, specially those introduced in #7239.

This PR allow truncation of those that are fine.

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📚 Documentation preview 📚: https://pymc--7476.org.readthedocs.build/en/7476/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.16%. Comparing base (799c98f) to head (ba61d12).
Report is 100 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7476      +/-   ##
==========================================
- Coverage   92.17%   92.16%   -0.01%     
==========================================
  Files         103      103              
  Lines       17217    17214       -3     
==========================================
- Hits        15869    15866       -3     
  Misses       1348     1348              

Files with missing lines	Coverage Δ
pymc/distributions/censored.py	100.00% <100.00%> (ø)
pymc/distributions/continuous.py	97.91% <100.00%> (ø)
pymc/distributions/truncated.py	99.45% <100.00%> (-0.01%)	⬇️

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