pip -> uv

[dakinggg]

Replace pip with uv. This reduces the time every action takes by 3-4 minutes because uv is just that much faster at installing things. Tested this PR against LLM Foundry (last commit here) and an internal repo to ensure it works. I do not fully understand the specific incantations that were needed to get everything to install correctly...but it does seem to work.

[eitanturok]

Two comments:

1. uv also supports virtual environments: https://docs.astral.sh/uv/pip/environments/. This should be faster than using python -m venv ../.venv
2. You currently install uv with pip install uv. But you can install uv without needing python as a dependency, curl -LsSf https://astral.sh/uv/install.sh | sh.

[snarayan21]

uv requires venv, so these changes seem sensible

a bit confused why we need site packages but that seems minor

approving to unblock but would be good to resolve that small q

[dakinggg]

@eitanturok both your statements are true, I was just trying to do the simplest change that would have benefit because making CI changes is difficult and annoying.

[mvpatel2000]

ok we ball

[b-chu]

Thanks!