function handleClick() {
  startTransition(() => {
    // ここで優先度の低い状態更新を行う
    setState(newState);
  });
}
console.log(1);
startTransition(() => {
  console.log(2);
  setPage('/about');
});
console.log(3);
import { startTransition } from 'react';
const [isPending, startTransition] = useTransition();