Methods adding intervals to CalDateTime should have identical logic for setting the IDateTime result

[axunonb]

In the CalDateTime class, methods that return an IDateTime by adding ticks, minutes, seconds, and other time intervals will set the IDateTime.HasTime property to true if the resulting date-time value is not a multiple of full days. This ensures that the IDateTime instance correctly reflects whether it includes a time component.

The methods are:

• AddTicks(long ticks)
• AddMilliseconds(int milliseconds)
• AddSeconds(int seconds)
• AddMinutes(int minutes)
• AddHours(int hours)
• AddDays(int days)
• AddMonths(int months)
• AddYears(int years)
• Add(TimeSpan ts)
• Subtract(TimeSpan ts)

These methods should set the IDateTime.HasTime property to true if the resulting date-time value includes a time component. Specifically, if the added interval results in a date-time value that is not a multiple of full days (i.e., it includes hours, minutes, seconds, or smaller units), the HasTime property should be set to true. This ensures that the IDateTime instance accurately represents whether it includes a time component.

CalDateTime dateTime = new CalDateTime(new DateTime(2023, 10, 1));
dateTime.HasTime = false;

// Adding 1 hour to the date-time value
IDateTime newDateTime = dateTime.AddHours(1);

// The resulting date-time value includes a time component, so HasTime is set to true
Assert.That(newDateTime.HasTime, Is.True);