More informative error message for unused step sampler arguments

[jahall]

More informative error message when passing invalid kwargs to sample

Bugfixes

Closes #6737

---

📚 Documentation preview 📚: https://pymc--6738.org.readthedocs.build/en/6738/

[ricardoV94]

This looks great!

[codecov]

Codecov Report

Merging #6738 (483cd5e) into main (0073639) will decrease coverage by 0.06%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6738      +/-   ##
==========================================
- Coverage   91.99%   91.93%   -0.06%     
==========================================
  Files          95       95              
  Lines       16180    16128      -52     
==========================================
- Hits        14885    14828      -57     
- Misses       1295     1300       +5     

Impacted Files	Coverage Δ
pymc/sampling/mcmc.py	89.88% <100.00%> (+0.06%)	⬆️
pymc/step_methods/compound.py	97.63% <100.00%> (ø)

... and 25 files with indirect coverage changes

[jahall]

@ricardoV94 Fixed mypy issues now...but went down a small rabbit hole to add type hints to assign_step_methods

[welcome]

Congrats on merging your first pull request! 🎉 We here at PyMC are proud of you! 💖 Thank you so much for your contribution 🎁