Wire with_remote_overrides to construct model families (#7621)

- This PR wires `with_remote_overrides` and make the
`construct_model_families` an async function
- Moves getting model family a level above to keep the function `sync`
- Updates the tests to local, offline, and `sync` helper for model
families

codex-rs/tui/src/app_backtrack.rs

@@ -340,6 +340,7 @@ impl App {
         let session_configured = new_conv.session_configured;
         let init = crate::chatwidget::ChatWidgetInit {
             config: cfg,
+            model_family: self.chat_widget.get_model_family(),
             frame_requester: tui.frame_requester(),
             app_event_tx: self.app_event_tx.clone(),
             initial_prompt: None,