`chunkedgraph` module documentation improvements and standardization

[bdpedigo]

Summary

• Added documentation for some returns which have a dictionary with many fields or dataframe etc.
  • This was my main reason for this PR, as a new user I just found the meaning of many of these kinds of returns opaque.
  • This could probably still be improved. I took a stab at documenting these fields but if I could be wrong, feel free to add corrections.
• Made everything use numpydoc, previously it was a mix
• Used a more standard way of specifying types (see numpydoc)
• Clarified references to actual variables in the docstrings with backticks
• Added a few missing param descriptions
• Tried to standardize nomenclature a bit, at least in this module

TODO

• [x] fix remaining inline TODOs about clarifying units
  • asked for feedback on a couple
• [x] build docs locally to test

[bdpedigo]

I think I've addressed everything - but lmk if any further changes are requested