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.

crates/uv-client/src/error.rs

@@ -148,8 +148,8 @@ pub enum ErrorKind {
     #[error("Expected an index URL, but received non-base URL: {0}")]
     CannotBeABase(Url),
 
-    #[error(transparent)]
-    DistInfo(#[from] install_wheel_rs::Error),
+    #[error("Failed to read metadata: `{0}`")]
+    Metadata(String, #[source] uv_metadata::Error),
 
     #[error("{0} isn't available locally, but making network requests to registries was banned")]
     NoIndex(String),