Refresh on models etag mismatch (#8491)

- Send models etag
- Refresh models on 412
- This wires `ModelsManager` to `ModelFamily` so we don't mutate it
mid-turn

codex-rs/codex-api/tests/models_integration.rs

@@ -86,7 +86,6 @@ async fn models_client_hits_models_endpoint() {
             context_window: None,
             experimental_supported_tools: Vec::new(),
         }],
-        etag: String::new(),
     };
 
     Mock::given(method("GET"))
@@ -102,13 +101,13 @@ async fn models_client_hits_models_endpoint() {
     let transport = ReqwestTransport::new(reqwest::Client::new());
     let client = ModelsClient::new(transport, provider(&base_url), DummyAuth);
 
-    let result = client
+    let (models, _) = client
         .list_models("0.1.0", HeaderMap::new())
         .await
         .expect("models request should succeed");
 
-    assert_eq!(result.models.len(), 1);
-    assert_eq!(result.models[0].slug, "gpt-test");
+    assert_eq!(models.len(), 1);
+    assert_eq!(models[0].slug, "gpt-test");
 
     let received = server
         .received_requests()