fix: incorrect timestamp inserted to duckdb

[yeahbai08]

educkdb inserted an incorrect timestamp to database.

DuckDB represents instants as the number of microseconds (µs) (or nanoseconds, for TIMESTAMP_NS) since 1970-01-01 00:00:00+00.

https://duckdb.org/docs/sql/data_types/timestamp

[mmzeeman]

The epoch is there to make it easier to insert timestamps from erlang. In Erlang timestamps are usually made in Gregorian days. See: https://www.erlang.org/doc/apps/stdlib/calendar.html