Added a comment to emphasize that the purpose of this demo extension is to highlight a potential bug inside libcql. As far as I know libcql is meant to be thread safe, but this demo
shows otherwise. A bunch of concurrent calls to pool->query() inevitably result in an exception "The associated promise has been destructed prior to the associated state becoming ready."

Hopefully, this will get the community interested in helping me debugging the demo and underlying libcql calls...