Microseconds to date converter

Converts a sixteen-digit microsecond timestamp into a date. PostgreSQL stores timestamps at microsecond resolution internally, and Python’s `time.time_ns()` divided by a thousand gives the same.

Microseconds show up most often when a value has come straight out of a database rather than through an application layer. PostgreSQL’s internal representation is microseconds since 2000-01-01, which is a different epoch again — a raw pg value needs the epoch shift as well as the unit change, and a value that decodes to 2053 is a Postgres-epoch number being read as a Unix one. Worth knowing that a JavaScript `Date` cannot hold microsecond precision at all: converting to one silently discards the last three digits, so a round trip through JavaScript loses resolution you may be relying on for ordering.