Test if a date falls inside a leap month
A month is a leap month (闰月) if it does not contain a major solar term (中气). This happens when two new moons fall within the same major solar term period.
Calendar configuration
Julian Ephemeris Day (any day within the month)
true if the month containing this date is a leap month
Low-level pure functions for calendar conversion. Most users should prefer the ChineseDate value object API. These functions are useful when you need fine-grained control or want to build custom logic on top of the core algorithms.