date time functions (#425)

* merge networkdays, networkdays.intl #33

* merge time, timevalue, hour, minute, second #35

* merge datedif, datevalue #36

* merge days, days360, weekday, weeknum, workday, workday.intl, yearfrac, isoweeknum #41

* from excel helper

* fix build

* date time macros

* de-dupe weekend

* serial helper

* de-dupe now today

* weekend pattern enum

* remove unused clippy wrong self

* fix docs

* add test coverage

* fix build

* fix cursor comment

* PR coments + xlsx date time

base/src/test/test_days360_month_end.rs

@@ -0,0 +1,43 @@
+use crate::test::util::new_empty_model;
+
+#[test]
+fn test_days360_month_end_us() {
+    let mut model = new_empty_model();
+
+    // 31 Jan 2021 -> 28 Feb 2021 (non-leap)
+    model._set("A1", "=DAYS360(DATE(2021,1,31),DATE(2021,2,28))");
+
+    // 31 Jan 2020 -> 28 Feb 2020 (leap year – not last day of Feb)
+    model._set("A2", "=DAYS360(DATE(2020,1,31),DATE(2020,2,28))");
+
+    // 28 Feb 2020 -> 31 Mar 2020 (leap year span crossing month ends)
+    model._set("A3", "=DAYS360(DATE(2020,2,28),DATE(2020,3,31))");
+
+    // 30 Apr 2021 -> 31 May 2021 (end-of-month adjustment rule)
+    model._set("A4", "=DAYS360(DATE(2021,4,30),DATE(2021,5,31))");
+
+    model.evaluate();
+
+    assert_eq!(model._get_text("A1"), *"30");
+    assert_eq!(model._get_text("A2"), *"28");
+    assert_eq!(model._get_text("A3"), *"33");
+    assert_eq!(model._get_text("A4"), *"30");
+}
+
+#[test]
+fn test_days360_month_end_european() {
+    let mut model = new_empty_model();
+
+    // European basis = TRUE (or 1)
+    model._set("B1", "=DAYS360(DATE(2021,1,31),DATE(2021,2,28),TRUE)");
+
+    model._set("B2", "=DAYS360(DATE(2020,1,31),DATE(2020,2,29),TRUE)");
+
+    model._set("B3", "=DAYS360(DATE(2021,8,31),DATE(2021,9,30),TRUE)");
+
+    model.evaluate();
+
+    assert_eq!(model._get_text("B1"), *"28");
+    assert_eq!(model._get_text("B2"), *"29");
+    assert_eq!(model._get_text("B3"), *"30");
+}