Have a "/refreshEventStats" endpoint, only accessible to event organizers (request a family public token access for it), and triggering an event stats calculation + persistence in a dedicated collection (only if some favorites/feedback's last-update has changed since previous generation)
Change /publicEventStats endpoint to rely on this new collection only
Instead, we should split things in 2:
last-updatehas changed since previous generation)/publicEventStatsendpoint to rely on this new collection onlyThis new collection will be useful for #55