read-as-instant (clj)

After calling this function, `next.jdbc.result-set/ReadableColumn` will be extended to (`java.sql.Date` and) `java.sql.Timestamp` so that any timestamp columns will automatically be read as `java.time.Instant`. Note that `java.sql.Date` columns will still be returned as-is because they cannot be converted to an instant (they lack a time component).