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/thread-manager-sample/src/main.rs

@@ -55,6 +55,7 @@ use codex_core_api::UriBasedFileOpener;
 use codex_core_api::UserInput;
 use codex_core_api::WebSearchMode;
 use codex_core_api::arg0_dispatch_or_else;
+use codex_core_api::build_models_manager;
 use codex_core_api::built_in_model_providers;
 use codex_core_api::find_codex_home;
 use codex_core_api::init_state_db;
@@ -132,7 +133,8 @@ async fn run_main(arg0_paths: Arg0DispatchPaths) -> anyhow::Result<()> {
     });
     let thread_manager = ThreadManager::new(
         &config,
-        auth_manager,
+        Arc::clone(&auth_manager),
+        build_models_manager(&config, auth_manager),
         SessionSource::Exec,
         environment_manager,
         Arc::new(extensions.build()),