Add complete dask compatibility testing

[anissa111]

PR Summary

• Expands tests/test_dask.py to test all functions under geocat-comp (except name aliases, internal functions, and functions that just wrap other geocat-comp functions)
  • notes if existing functions are not currently compatible by having a test, but marking it as an expected failure
• Adds a conftest.py to handle some pytest fixtures so they can be used in multiple test files, reconfigures some existing fixtures to live in conftest.py
• makes small changes to relhum_water and relhum_ice to make them dask compatible
• reformats a couple places where black was forcing 1 item/line lists that were really annoying

Related Tickets & Documents

Closes https://github.com/NCAR/geocat-planning/issues/27

PR Checklist

General

• PR includes a summary of changes
• Link relevant issues, make one if none exist
• Add a brief summary of changes to docs/release-notes.rst in a relevant section for the upcoming release.
• Add appropriate labels to this PR
• PR follows the Contributor's Guide

[kafitzgerald]

This looks good to me!

Will be nice to have this all documented (i.e. the xfails) and easily testable.

I'd forgotten (or maybe just didn't know) how many things weren't compatible.