bug: fix model save (#3525)

Fix those 2 behaviors:
1. The model does not get saved if we don't CTRL + S
2. The reasoning effort get saved

codex-rs/core/tests/suite/mod.rs

@@ -7,6 +7,7 @@ mod exec;
 mod exec_stream_events;
 mod fork_conversation;
 mod live_cli;
+mod model_overrides;
 mod prompt_caching;
 mod seatbelt;
 mod stream_error_allows_next_turn;