Prevent infinite loops from zero-interval DatePeriods

[dereuromark]

Summary

• Adds validation to ChronosPeriod and ChronosDatePeriod constructors to throw InvalidArgumentException when given a DatePeriod with a zero interval
• Prevents infinite loops that crash the server when iterating over such periods

The Problem

Creating a ChronosPeriod with a zero interval causes an infinite loop:

$period = new DatePeriod(
    new DateTime('2025-01-01'),
    new DateInterval('PT0S'),  // Zero seconds!
    new DateTime('2025-01-02')
);

// This causes an infinite loop - the iterator never advances
foreach (new ChronosPeriod($period) as $date) {
    // Server crash...
}

The Fix

The constructor now validates the interval and throws an exception:

// Now throws InvalidArgumentException
new ChronosPeriod($period);
// "Cannot create a period with a zero interval. This would cause an infinite loop when iterating."

Related

Similar issue was reported for Carbon: briannesbitt/Carbon#3259