Implement unconditional constant_folding rewrite

[ricardoV94]

The existing constant_folding makes use of Op.do_constant_folding to decide whether to apply itself or not, even when all inputs are constant. This is a hackish way of trying to not perform constant_folding in cases where it may lead to a sub-optimal graph (basically requiring extra copies). It is also used for rewrites to have a chance to apply themselves.

This PR adds a constant_folding helper that does not follow this logic. It is not registered in the database. It's meant for advanced users / libraries to force constant_folding whenever it it is actually possible to.

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📚 Documentation preview 📚: https://pytensor--1068.org.readthedocs.build/en/1068/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.95%. Comparing base (e73258b) to head (560f41e).
Report is 97 commits behind head on main.

Additional details and impacted files

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  Coverage   81.95%   81.95%           
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  Files         182      182           
  Lines       47866    47870    +4     
  Branches     8622     8622           
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+ Hits        39228    39232    +4     
  Misses       6472     6472           
  Partials     2166     2166           

Files with missing lines	Coverage Δ
pytensor/tensor/rewriting/basic.py	94.15% <100.00%> (+0.03%)	⬆️