Set priority for prek to enable concurrent execution (#22506)
## Summary
prek allows you to set priorities, and can run tasks of the same
priority concurrently (e.g., we can run Ruff's Python formatting and
`cargo fmt` at the same time). On my machine, this takes `uvx prek run
-a` from 19.4s to 5.0s (~a 4x speed-up).
