Move sleep items to the extension-owned lifecycle path (#33159)

## What changed

- Define `SleepItem` in `codex-extension-items` and carry `clock.sleep` events through `TurnItem::Extension`.
- Preserve sleep persistence, thread-history reconstruction, and the app-server's `type: "sleep"` schema while reusing the extension-owned type.

## Testing

- Add serialization coverage for the `clock.sleep` extension wire shape and its protocol wrapper.
- Update sleep lifecycle and thread-history tests to exercise the extension-owned item.

GitOrigin-RevId: 34bb33ed9b90a09bf4744aafdb56e019c717a168

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

@@ -199,7 +199,7 @@ impl ChatWidget {
             }),
             item @ ThreadItem::SubAgentActivity { .. } => self.on_sub_agent_activity(item),
             ThreadItem::DynamicToolCall { .. } => {}
-            ThreadItem::Sleep { .. } => {}
+            ThreadItem::Sleep(_) => {}
         }
 
         if matches!(replay_kind, Some(ReplayKind::ThreadSnapshot)) && turn_id.is_empty() {