Extract METADATA reading into a crate (#7231)
This is preparatory work for the upload functionality, which needs to
read the METADATA file and attach its parsed contents to the POST
request: We move finding the `.dist-info` from `install-wheel-rs` and
`uv-client` to a new `uv-metadata` crate, so it can be shared with the
publish crate.
I don't properly know if its the right place since the upload code isn't
ready, but i'm PR-ing it now because it already had merge conflicts.