Cron expression, interval in ms, or one-shot delay in ms (as a string). A cron task
with a time zone stores TZ=<zone> <cron> (an opaque string for the store).
Epoch ms of the next occurrence; null once a one-shot task has run (a tombstone).
OptionallastOptionallastBumped by every successful ScheduleStore.claimDue; starts at 0 for a new id.
Never goes backwards for an id, even across delete and a new register.
OptionalleaseOptionallease
Persisted state of one durable task.