Create conda packages from sdist rather than git archives #2715

As cuda-python is a metapackage that combines multiple packages in a monorepo, it is fundamentally incompatible with releasing from a git archive, which may have only one version. Ideally, it would have access to all three versions (cuda-bindings, cuda-core and cuda-pathfinder) and be able to set up its dependencies automatically.

It should be possible to do this from an sdist (where we can inject whatever metadata we want based on tags at sdist-build-time). It is not possible from a git archive, where there is no way to inject metadata beyond what git allows into the tarball.

We should investigate where it is possible to stop supporting git archive. This is currently used for our conda package workflow, but that could probably be modified to expect an sdist instead.