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/thread_manager.rs

@@ -305,6 +305,7 @@ impl ThreadManager {
     pub fn new(
         config: &Config,
         auth_manager: Arc<AuthManager>,
+        models_manager: SharedModelsManager,
         session_source: SessionSource,
         environment_manager: Arc<EnvironmentManager>,
         extensions: Arc<ExtensionRegistry<Config>>,
@@ -337,7 +338,7 @@ impl ThreadManager {
             state: Arc::new(ThreadManagerState {
                 threads: Arc::new(RwLock::new(HashMap::new())),
                 thread_created_tx,
-                models_manager: build_models_manager(config, auth_manager.clone()),
+                models_manager,
                 environment_manager,
                 skills_service,
                 plugins_manager,