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/mcp-server/src/message_processor.rs

@@ -74,7 +74,8 @@ impl MessageProcessor {
         );
         let thread_manager = Arc::new(ThreadManager::new(
             config.as_ref(),
-            auth_manager,
+            Arc::clone(&auth_manager),
+            codex_core::build_models_manager(config.as_ref(), auth_manager),
             SessionSource::Mcp,
             environment_manager,
             Arc::new(extensions.build()),