Ensure authentication is passed from the index url to distribution files (#1886)

Closes https://github.com/astral-sh/uv/issues/1709
Closes https://github.com/astral-sh/uv/issues/1371

Tested with the reproduction provided in #1709 which gets past the HTTP
401.

Reuses the same copying logic we introduced in
https://github.com/astral-sh/uv/pull/1874 to ensure authentication is
attached to file URLs with a realm that matches that of the index. I had
to move the authentication logic into a new crate so it could be used in
`distribution-types`.

We will want to something more robust in the future, like track all
realms with authentication in a central store and perform lookups there.
That's what `pip` does and it allows consolidation of logic like netrc
lookups. That refactor feels significant though, and I'd like to get
this fixed ASAP so this is a minimal fix.

crates/uv-client/src/lib.rs

@@ -7,7 +7,6 @@ pub use registry_client::{
 };
 pub use rkyvutil::OwnedArchive;
 
-mod auth;
 mod cached_client;
 mod error;
 mod flat_index;