feat(networking): surface AuthenticationExpired for unrecoverable OAuth logins

[nichmor]

Description

Builds on the OAuth refresh handling already in main (OAuthRefreshOutcome /
OAuthRefreshFailure, which drops an expired access token when it cannot be
refreshed and sends the request unauthenticated so the auth-challenge
middleware can take over).

This adds a typed AuthenticationExpired { host } error for the case where
the stored login itself is no longer usable. In AuthenticationMiddleware:

• after a refresh attempt, inspect refresh_result.failure() and treat only
  MissingRefreshToken and ReauthenticationRequired as "the login is dead"
  (transient refresh problems keep the existing log-and-continue behavior);
• only when the dead credential was actually dropped (so the request goes out
  unauthenticated) remember the host;
• if that request still comes back 401/403, return
  AuthenticationExpired { host } so callers can prompt the user to
  re-authenticate (e.g. re-run their login command).

AuthenticationExpired is re-exported from the crate root.

How Has This Been Tested?

• pixi run cargo-fmt and pixi run -- cargo clippy -p rattler_networking --all-targets are clean.
• Relies on the existing oauth_refresh / authentication_middleware unit
  tests in main for the refresh-outcome paths.

pixi run -- cargo nextest run -p rattler_networking

Opened as a draft: no test yet asserts the new AuthenticationExpired
path end to end — happy to add one before marking ready.

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.

Tools: Claude (Claude Code, Opus 4.8)

what we have done in this branch?
can you create a draft pr?
ok, just make this branch to be exactly the same as main for now
can you push it again? I've made some changes there

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added sufficient tests to cover my changes.