this PR changes the v2 rule syntax to use python 3

async

and

await

so v2 engine `@rule`s can suddenly now be checked with my mypy! it's also green on CI! will let that simmer as long as it needs to but i'm super excited about this change! https://github.com/pantsbuild/pants/pull/8639

I think it’s ready for merge! There may be some follow up, like possibly renaming

MultiGet

, but this is great to land now. I just re-read the PR and code looks solid.

🚢