fix(app-server): mark thread/turns/list and exclude_turns as experime… (#20499)

…ntal

We have some bugs to work out and it is not quite ready to consume as a
public API.

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -564,6 +564,7 @@ client_request_definitions! {
         serialization: thread_id(params.thread_id),
         response: v2::ThreadReadResponse,
     },
+    #[experimental("thread/turns/list")]
     ThreadTurnsList => "thread/turns/list" {
         params: v2::ThreadTurnsListParams,
         // Explicitly concurrent: this primarily reads append-only rollout storage.