Function civil_from_unix_nanos 

pub fn civil_from_unix_nanos(ns: i64) -> CivilDateTime

Decompose a SmoothUTC instant (nanoseconds since 1970-01-01T00:00:00) into its civil date-time. Floor division makes pre-epoch instants correct (e.g. -1 ns is 1969-12-31T23:59:59.999999999).