Investigate using uv instead of pip in CI

[vyasr]

uv installs packages faster than pip and would potentially result in meaningfully faster builds (especially if eventually coupled with a package cache as discussed in #51). However, uv does have some noted incompatibilities with pip behavior that we will need to consider, such as the direct reference issue noted in #85. We can't use uv quite yet, but once #85 is resolved it would be worthwhile testing it out to see how close we are.