snowflake libraries generally aren't updated after they're stabilized

- it only looks at system time at system startup, then relies on instant for monotonic clock source. unfortunately for setups that do leap-second smearing (ours does), this would deviate slightly out of sync after operating for a while.

- does not handle seq overflow within a given millisecond window - this i think is very unsafe, and can cause the generation of duplicate IDs if `next_id` is called at too rapid an interval.