Create a `piker` coding style guide?

[goodboy]

We've run up against this a buncha times now as the contrib set has
grown and i probably shouldn't have to keep restating it vs. just
linking to our preferences 😂

Not sure exactly where to stick it but the short list is:

• doc strings use the whole ''' + extra NL before closing '''
• use multi-line func sigs wherever we have >= N arguments
• organize imports into 3 sections: stdlib, 3rd party, internal
• add ruff to CI:
  • https://beta.ruff.rs/docs/editor-integrations/#github-actions
  • https://beta.ruff.rs/docs/usage/#github-action