pub fn wait(self) -> Result<(), EspNowError> {
        // prevent redundant waiting since we waits for the callback in the Drop
        // implementation
        core::mem::forget(self);
        while !ESP_NOW_SEND_CB_INVOKED.load(Ordering::Acquire) {}

        if ESP_NOW_SEND_STATUS.load(Ordering::Relaxed) {
            Ok(())
        } else {
            Err(EspNowError::SendFailed)
        }
    }
Wait for the previous sending to complete, i.e. the send callback is
invoked with status of the sending.
esp-wifi/src/esp_now/mod.rs