The peers query read the nickname of every remote user every minute
(2.7 s and 1.2M buffer hits on a large instance). The instances table
now has a row for every host we know users from, so read it instead,
and recompute the stats every 5 minutes.
Based on Akkoma 138b1aea2 and 7b76fdeed.
Co-authored-by: Oneric <oneric@oneric.stub>
Co-authored-by: FloatingGhost <hannah@coffee-and-dreams.uk>
