Add type hints to dist() for discrete distributions

[johanbog]

What is this PR about? Add type hints to the dist() class methods in the discrete distributions. Issue https://github.com/pymc-devs/pymc/issues/5358

Discussion points:

• I am not sure if the type hints are correct for the cutpoints parameter in OrderedProbit and OrderedLogistic
• I believe that the type hints should also include list[Union[int, float]] (or list[int], in the cases where ints are expected), but that would require changing the implementation of typing for the continuous distributions as well, so I can do that in a separate PR if it should be done.

Checklist

• [x] Explain important implementation details 👆
• [x] Make sure that the pre-commit linting/style checks pass.
• [x] Link relevant issues (preferably in nice commit messages)
• [x] Are the changes covered by tests and docstrings?
• [x] Fill out the short summary sections 👇

Major / Breaking Changes

N/A

New features

N/A

Bugfixes

N/A

Documentation

N/A

Maintenance

N/A

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:books: Documentation preview :books:: https://pymc--6937.org.readthedocs.build/en/6937/

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.02%. Comparing base (46f1675) to head (2c01984).

:exclamation: Current head 2c01984 differs from pull request most recent head 6f6b416. Consider uploading reports for the commit 6f6b416 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6937      +/-   ##
==========================================
- Coverage   89.60%   89.02%   -0.59%     
==========================================
  Files         100      100              
  Lines       16888    16855      -33     
==========================================
- Hits        15133    15005     -128     
- Misses       1755     1850      +95     

Files	Coverage Δ
pymc/distributions/discrete.py	99.12% <100.00%> (+30.28%)	:arrow_up:

... and 80 files with indirect coverage changes

[thomasaarholt]

I originally made some comments on this PR, which I then turned into a feature request that I am willing to work on, over at #7122.