The one static Oban.Plugins.Cron entry ({"* * * * *", ScheduleTickWorker}). The cron
leader inserts one tick job per minute for the whole cluster. The tick accounts for settled
runs and enqueues a SuperPi.Workers.ScheduleRunWorker job for each due schedule
(SuperPi.Schedule.tick/1).
max_attempts: 1: a lost tick is repaired by the next one, which finds the same due rows.