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.

---

📚 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

@@ Coverage Diff @@ ## main #1068 +/- ## ======================================= Coverage 81.95% 81.95% ======================================= Files 182 182 Lines 47866 47870 +4 Branches 8622 8622 ======================================= + 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%)	⬆️