Do note that systemd does have a tmpfiles.d (terrible name nowadays, but that is besides the point) drop-in with an extra service that will clean out /var/tmp/ of unused files when they haven't been accessed within 30 days (all of a/m/ctime are checked). Same applies to /tmp/ but with 10 days. I don't know if the service is enable by default on any distros though, so assume it is unless otherwise ensured :)
