Primitive proleptic Gregorian date helpers.

These helpers keep calendar dates explicit and deterministic without adding timezone handling.

Examples

use use_date::{CalendarDate, add_days, day_of_year, days_between, is_valid_date};

let leap_day = CalendarDate::new(2024, 2, 29).unwrap();
let next_day = add_days(leap_day, 1);

assert!(is_valid_date(2024, 2, 29));
assert_eq!(day_of_year(2024, 2, 29).unwrap(), 60);
assert_eq!(next_day, CalendarDate::new(2024, 3, 1).unwrap());
assert_eq!(days_between(leap_day, next_day), 1);