Merge redundant code across logprob, pytensorf and distributions/transform

[ricardoV94]

Helps with #6908
Closes #6859

Also gets rid of some annoying circular imports

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📚 Documentation preview 📚: https://pymc--6976.org.readthedocs.build/en/6976/

[codecov]

Codecov Report

Merging #6976 (322b3d3) into main (ad450a6) will decrease coverage by 7.54%.
The diff coverage is 96.02%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6976      +/-   ##
==========================================
- Coverage   87.66%   80.12%   -7.54%     
==========================================
  Files         101      101              
  Lines       16964    16858     -106     
==========================================
- Hits        14871    13507    -1364     
- Misses       2093     3351    +1258     

Files	Coverage Δ
pymc/gp/cov.py	98.00% <100.00%> (ø)
pymc/gp/util.py	96.47% <100.00%> (+0.04%)	⬆️
pymc/initial_point.py	94.05% <100.00%> (-5.95%)	⬇️
pymc/logprob/basic.py	79.57% <100.00%> (-6.95%)	⬇️
pymc/logprob/checks.py	45.83% <100.00%> (+2.08%)	⬆️
pymc/logprob/mixture.py	24.33% <100.00%> (-4.62%)	⬇️
pymc/logprob/scan.py	18.09% <100.00%> (-73.37%)	⬇️
pymc/logprob/tensor.py	50.43% <100.00%> (+0.43%)	⬆️
pymc/logprob/transform_value.py	73.75% <100.00%> (ø)
pymc/logprob/transforms.py	55.74% <100.00%> (-12.01%)	⬇️
... and 7 more

... and 30 files with indirect coverage changes

[ricardoV94]

Converted to draft as there are two bugfix PRs that involve transforms and will certainly conflict with this one

[ricardoV94]

Ready for review again.

I am still divided about what to do with the custom Transforms implemented in distributions/transforms.py so I am leaving them there for now. I am not sure where they should live, if there or in logprob/transforms.py or perhaps logprob/transform_value.py?

I am more inclined for the latter, but for now I just removed duplicated functionality (Chain vs ChainedTransform) and left everything in the same place.