Allow injecting the models manager into ThreadManager (#32911)

## Why

Embedding callers need to control whether model catalogs are persisted to disk.

## What changed

- Accept a shared models manager when constructing `ThreadManager` instead of always creating a cached manager internally.
- Add provider APIs for creating uncached model managers. OpenAI-compatible providers fetch on each `OnlineIfUncached` refresh without reading or writing `models_cache.json`.
- Keep existing app server, MCP server, sample, and test callers on the standard cached manager.

## Testing

- Verify an uncached manager fetches on every refresh.
- Verify an injected uncached manager controls thread refresh behavior and does not create `models_cache.json`.

GitOrigin-RevId: 8bb646054ecec4ccb865b2bf56249384916ea9db

codex-rs/core/src/agent/control_tests.rs

@@ -2393,9 +2393,11 @@ async fn spawn_thread_subagent_uses_role_specific_nickname_candidates() {
 async fn resume_thread_subagent_restores_stored_metadata() {
     let (home, config) = test_config().await;
     let thread_store = Arc::new(InMemoryThreadStore::default());
+    let auth_manager = AuthManager::from_auth_for_testing(CodexAuth::from_api_key("dummy"));
     let manager = ThreadManager::new(
         &config,
-        AuthManager::from_auth_for_testing(CodexAuth::from_api_key("dummy")),
+        auth_manager.clone(),
+        crate::thread_manager::build_models_manager(&config, auth_manager),
         SessionSource::Exec,
         Arc::new(codex_exec_server::EnvironmentManager::default_for_tests()),
         empty_extension_registry(),