Added type hints to discrete distributions in pymc/distributions/discrete.pyAdd type hints to discrete distributions

[deveshbervar]

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📚 Documentation preview 📚: https://pymc--7701.org.readthedocs.build/en/7701/

[welcome]

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[OriolAbril]

I don't know what the DIST_PARAMETER_TYPES is supposed to be nor I can find it defined anywhere. Would you care to elaborate on the goal of the PR? Otherwise we'll have to close it