Function date_plus_duration 

pub fn date_plus_duration(date: i64, dur: &DurationValue) -> i64

date + duration (#920): only date-precision components apply — add the signed months then days. The duration’s sub-day time is ignored (a date has no time-of-day; openCypher does not carry it into days). Returns the date (i64 days), range-complete via crate::calendar (#1011).