Require auth managers to receive routing configuration (#34650)

## Why

Auth managers should use the application's resolved HTTP client factory instead
of silently falling back to the transport's default proxy behavior.

## What changed

- Make `AuthRouteConfig` required when constructing an `AuthManager` or
  `AuthConfig`.
- Pass each production caller's resolved routing configuration through without
  wrapping it in an optional value.
- Add a test helper that explicitly selects the transport-default proxy policy
  for callers that do not exercise custom routing.

GitOrigin-RevId: d89a3b1f8b5d4007650cdac0aae241c94d598580

codex-rs/login/tests/suite/auth_refresh.rs

@@ -1220,7 +1220,7 @@ impl RefreshTokenTestContext {
             /*forced_chatgpt_workspace_id*/ None,
             /*chatgpt_base_url*/ None,
             AuthKeyringBackendKind::default(),
-            /*auth_route_config*/ None,
+            codex_login::test_support::transport_default_auth_route_config(),
         )
         .await;
 

codex-rs/login/tests/suite/logout.rs

@@ -207,7 +207,7 @@ async fn auth_manager_logout_with_revoke_uses_cached_auth() -> Result<()> {
         /*forced_chatgpt_workspace_id*/ None,
         /*chatgpt_base_url*/ None,
         AuthKeyringBackendKind::default(),
-        /*auth_route_config*/ None,
+        codex_login::test_support::transport_default_auth_route_config(),
     )
     .await;
     save_auth(