fn update_handler<F: FnMut(&Self) + Sync + Send + 'static>(mut f: F) {
        Self::handler().with(|handler| {
            let mut prev: Box<Handler<Self>> =
                handler.take().unwrap_or_else(default_handler::<Self>);
            handler.replace(Box::new(move |event| {
                prev(event);
                f(event)
            }));
        })
    }
Atomic combination of [`Self::take_handler`] and
[`Self::replace_handler`]. Use this to add a new handler which runs
after the previously registered handlers.
esp-wifi/src/wifi/event.rs