0.29 Release

I think we're probably ready to ship the 0.29 release soon, there are a quite a number of changes now merged on `main`. Some items which I would like to see done before release: - #5862 - this continues the work already done in #5809 and should improve build performance downstream - #5965 - we have a lot of FFI changes in this release and it'd be great to audit the FFI as much as we can before shipping - #5944 - looks like a small and obvious cleanup - #5904 - getting this CLI packaged for the release will get us a workable introspection pipeline for `setuptools-rust` users Fellow maintainers, anything else you would ideally like to see shipped?