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/app-server/src/mcp_refresh.rs

@@ -226,6 +226,7 @@ mod tests {
             ThreadManager::new(
                 &good_config,
                 auth_manager.clone(),
+                codex_core::build_models_manager(&good_config, auth_manager.clone()),
                 SessionSource::Exec,
                 Arc::clone(&environment_manager),
                 thread_extensions(

codex-rs/app-server/src/message_processor.rs

@@ -262,6 +262,7 @@ impl MessageProcessor {
             ThreadManager::new(
                 config.as_ref(),
                 auth_manager.clone(),
+                codex_core::build_models_manager(config.as_ref(), auth_manager.clone()),
                 session_source,
                 environment_manager,
                 thread_extensions(