feat: reasoning effort as optional (#3527)

Allow the reasoning effort to be optional

codex-rs/tui/src/app_event.rs

@@ -46,7 +46,7 @@ pub(crate) enum AppEvent {
     CommitTick,
 
     /// Update the current reasoning effort in the running app and widget.
-    UpdateReasoningEffort(ReasoningEffort),
+    UpdateReasoningEffort(Option<ReasoningEffort>),
 
     /// Update the current model slug in the running app and widget.
     UpdateModel(String),