Move token usage/context information to session level (#3221)

Move context information into the main loop so it can be used to
interrupt the loop or start auto-compaction.

codex-rs/tui/src/chatwidget/tests.rs

@@ -221,8 +221,7 @@ fn make_chatwidget_manual() -> (
         active_exec_cell: None,
         config: cfg.clone(),
         initial_user_message: None,
-        total_token_usage: TokenUsage::default(),
-        last_token_usage: TokenUsage::default(),
+        token_info: None,
         stream: StreamController::new(cfg),
         running_commands: HashMap::new(),
         task_complete_pending: false,