chore(dev-deps): move to uv for development

[cpcloud]

Description of changes

This PR moves our dependency management over to uv.

Wanted to get a head start on CI and see what shakes out.

TODOs:

• uv2nix issue that needs to be fixed. This is fixed
• preserve existing dev versioning scheme (right now it's major.post$N.dev0).
• nix package builds (that's what runs tests in the nix.yml GHA workflows) aren't working at all right now not working the way I'd like, but tests are being run similarly to how they were under poetry2nix.
• release scripts need to be ported, but I think I can mostly keep them the same

[cpcloud]

I've opened pyproject-nix/pyproject.nix#173 for the pyproject.nix work, but that isn't necessary to merge this PR, we're still running tests in per-python-version isolated nix environments, we're just not doing it through the usual test-during-package-builds mechanism.

[cpcloud]

Ok, I've somewhat improved the nix builds. I'm still not sure if the way I did it is 100% kosher, but now the nix builds have the same behavior as before: they're testing ibis as part of a package build.

[adisbladis]

Ok, I've somewhat improved the nix builds. I'm still not sure if the way I did it is 100% kosher, but now the nix builds have the same behavior as before: they're testing ibis as part of a package build.

I've made of the uv2nix usage more idiomatic & tidied up the confusion re buildPythonPackage in cpcloud#27

[cpcloud]

Merging, so that I can work out any kinks in the cloud CI.