Add type hint to RandomVariable.rng_fn

[sujitpal]

Type hint added to RandomVariable.rng_fn based on pymc-devs/pymc#5326

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[brandonwillard]

Thanks for the addition!

[rlouf]

Rebased on main. This is mergeable provided the CI is all green.

[codecov]

Codecov Report

Merging #827 (9614f42) into main (aa5223c) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #827   +/-   ##
=======================================
  Coverage   74.09%   74.09%           
=======================================
  Files         174      174           
  Lines       48605    48605           
  Branches    10340    10340           
=======================================
  Hits        36014    36014           
  Misses      10305    10305           
  Partials     2286     2286           

Impacted Files	Coverage Δ
aesara/tensor/random/op.py	97.40% <100.00%> (ø)

[brandonwillard]

@sujitpal, thanks for the contribution!