RFC: Let's start vendoring dependencies

[schrockn]

Summary & Motivation

I am proposing that we start to default to vendoring dependencies whenever it is feasible. This will reduce our testing surface area and we are less likely to be thrashed by the Python ecosystem.

This just manually does this for now, but we could write some tooling support for this if necessary (automatically copy stuff down, don't ruff or typecheck the files, etc).

How I Tested These Changes

BK