This "works," but at no small cost:

1. Using the half-official binaries that zizmor's CI is producing means that we have pretty narrow glibc constraints, e.g. we can't run on ubuntu-22.04 or earlier because the binaries get built against a newer glibc.
2. It's not that much faster than just using setup-uv. Maybe a second or two faster at the absolute most, although perhaps that in turn could be improved with caching.
3. Windows is broken for unclear reasons.

(1) and (3) are annoying but not deal breakers, since this action will definitely have a "happy path" for newer runners and doesn't really need to support Windows runners (since they're significantly slower anyways). But (2) might be a deal breaker if I can't bring the performance up.

This was a good experiment, but the lack of an immediate perf boost + additional maintenance overhead makes it not super appealing in the short term. I'm going to experiment with #19 as another alternative approach here.