Cache lookups for EventUser on event creation
Cache lookups for EventUser on event creation

This ensures that low cardinality (or high throughput) scenarios defer most IntegrityError scenarios, which can become very common.

fotinakis/sentry,jean/sentry,daevaorn/sentry,zenefits/sentry,JackDanger/sentry,gencer/sentry,mitsuhiko/sentry,gencer/sentry,nicholasserra/sentry,JamesMura/sentry,mvaled/sentry,nicholasserra/sentry,jean/sentry,fotinakis/sentry,JamesMura/sentry,zenefits/sentry,fotinakis/sentry,alexm92/sentry,ifduyue/sentry,looker/sentry,looker/sentry,looker/sentry,zenefits/sentry,BuildingLink/sentry,gencer/sentry,mvaled/sentry,BuildingLink/sentry,ifduyue/sentry,fotinakis/sentry,gencer/sentry,daevaorn/sentry,mvaled/sentry,alexm92/sentry,daevaorn/sentry,mvaled/sentry,JamesMura/sentry,ifduyue/sentry,nicholasserra/sentry,mvaled/sentry,BuildingLink/sentry,JackDanger/sentry,beeftornado/sentry,jean/sentry,beeftornado/sentry,mvaled/sentry,JamesMura/sentry,BuildingLink/sentry,ifduyue/sentry,JamesMura/sentry,looker/sentry,jean/sentry,jean/sentry,daevaorn/sentry,looker/sentry,gencer/sentry,zenefits/sentry,beeftornado/sentry,JackDanger/sentry,alexm92/sentry,mitsuhiko/sentry,zenefits/sentry,ifduyue/sentry,BuildingLink/sentry