MNT/STY/TST: Add pre-commit hooks, CI job, standardize style

[tangkong]

Description

• adds pre-commit hooks and relevant .rc files to the repository
• adds github actions pre-commit job to run on pull requests
• (WIP) apply changes suggested by pre-commit (flake8, shellcheck, etc)
  • [x] python files ~- [ ] bash scripts (hooooo boy)~
• Converts some old py2 scripts to py3

Motivation and Context

The style is whack.

Shellcheck is a much larger effort, and one that we should be careful with. We'll have to go through those more carefully, but for now the CI will only check diff'd files

I spent way too much time trying to grab specific sha's for pre-commit's --from-ref and --to-ref arguments, but the location of that information in the github payload was inconsistent between push and pull-request. At that point I figured I should just get it working.

How Has This Been Tested?

Pre-commit vomits all over my terminal repeatedly

Where Has This Been Documented?

This PR