Closes this connection: drops the SQL #name temp tables it created, if any, and stops it sending requests. Closing a closed connection does nothing.
The drop goes through Self::drop_session, failing over as any request does; a failure is logged, not returned, since the server reclaims the session on its own. It is skipped where no temp table was created, and against a server that does not support session temp tables, which never reports one. A session given by KineticaOptions::session_id is not dropped: the caller drops it with Self::drop_session.
After this every request fails, at once and without failing over. The fail-back poller is stopped. A connection that is never closed has its session dropped when it is dropped, on a best-effort basis; closing it is what makes the drop prompt.