Update Makefile to check for uv pip

[robhudson]

One-line summary

If uv pip, use it, otherwise fall back to pip. This also pulls in the check-pinned-requirements.py instead of raw pip list.

• I used an AI to write some of this code.

AI helped spit out a skeleton of the check-pinned-requirements.py file and I further honed it.

[stevejalim]

r+

Sorry for the late review. Originally I wasn't sure enough of context and was short on headspace, but I've got my head around it now. This looks cool and should speed things up nicely in general.