Typehints and updated docstring for Blackjax NUTS sampling function

[jhrcook]

What is this PR about?

This PR adds typehints to the function pymc.sampling_jax.sample_blackjax_nuts function and updates the docstring with information for the initvals argument.

Checklist

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

Major / Breaking Changes

• None

Bugfixes / New features

• Add typehints to pymc.sampling_jax.sample_blackjax_nuts

Docs / Maintenance

• Add the argument initvals to the docstring of pymc.sampling_jax.sample_blackjax_nuts
• Reflow the docstring for pymc.sampling_jax.sample_blackjax_nuts

[codecov]

Codecov Report

Merging #6022 (7209c09) into main (7d960fa) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #6022   +/-   ##
=======================================
  Coverage   89.17%   89.17%           
=======================================
  Files          72       72           
  Lines       12901    12901           
=======================================
  Hits        11504    11504           
  Misses       1397     1397           

Impacted Files	Coverage Δ
pymc/sampling_jax.py	96.96% <100.00%> (ø)