isBetweenOrEqual method
Checks if the current DateTime object is between or equal to the given start and end DateTime objects.
Returns true
if the current DateTime is between the start and end DateTime ,
or if it is equal to the start or end DateTime. Otherwise, returns false
.
Implementation
bool isBetweenOrEqual(DateTime start, DateTime end) => isBetween(start, end) || this == start || this == end;