addDays method
Adds the specified number of days to the current DateTime.
Args: days (int): The number of days to add.
Returns: DateTime: A new DateTime object with the added days.
Implementation
DateTime addDays(int days) {
if (days == 0) {
// same
return this;
}
// We used the Jiffy package to add years, months, etc
// https://stackoverflow.com/questions/54792056/add-subtract-months-years-to-date-in-dart
return Jiffy.parseFromDateTime(this).add(days: days).dateTime;
}