Add return type hints

[michaelosthege]

Closes #4880

I know the ticket is about docstrings, but Sphinx can take the type information from the code automatically, so it should be enough to keep a single source of truth.

With this all functions in that file have annotated return types.

And in the end I just want to get the ticket out of the way.

[codecov]

Codecov Report

Merging #5819 (bb569e2) into main (4d2f3a8) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #5819      +/-   ##
==========================================
- Coverage   89.39%   89.37%   -0.02%     
==========================================
  Files          74       74              
  Lines       13767    13770       +3     
==========================================
  Hits        12307    12307              
- Misses       1460     1463       +3     

Impacted Files	Coverage Δ
pymc/distributions/distribution.py	90.83% <ø> (ø)
pymc/aesaraf.py	91.95% <100.00%> (+0.06%)	⬆️
pymc/distributions/logprob.py	97.65% <100.00%> (ø)
pymc/parallel_sampling.py	86.46% <0.00%> (-1.00%)	⬇️

[michaelosthege]

@ricardoV94 can I squash merge this?
Just to get it out of the way..

[michaelosthege]

@ricardoV94 can I squash merge this?
Just to get it out of the way..

[ricardoV94]

@ricardoV94 can I squash merge this? Just to get it out of the way..

Sure