[@mantine/dates] DateTimePicker: Set milliseconds to 0 on the result …

…date object (#7328)

This sets the milliseconds to 0.
Otherwise comparisons with Dates changed by the datetimepicker become very annoying.
For Example:

```new Date('2025-01-01T16:00+0100') >= <DatePickedWithDateTimePicker>``` is always false because of the milliseconds added.

packages/@mantine/dates/src/components/DateTimePicker/DateTimePicker.tsx

@@ -168,6 +168,7 @@ export const DateTimePicker = factory<DateTimePickerFactory>((_props, ref) => {
       timeDate.setHours(hours);
       timeDate.setMinutes(minutes);
       timeDate.setSeconds(seconds || 0);
+      timeDate.setMilliseconds(0);
       setValue(assignTime(timeDate, _value || shiftTimezone('add', new Date(), ctx.getTimezone())));
     }
   };