func (m Month) numDaysUnchecked(yy int) int {
	return bsDaysInMonthsByYear[yy][int(m)-1]
}
An unchecked variant of NumDays. This is only for private uses through the
Time struct when it is certain that the date in question is in range.
package nepcal
type Month int
const (
	Baisakh Month = 1 + iota
	Jestha
	Ashar
	Shrawan
	Bhadra
	Ashoj
	Kartik
	Mangshir
	Poush
	Magh
	Falgun
	Chaitra
)
func (m Month) NumDays(year int) (int, error) {
	if !IsInRangeYear(year) {
		return -1, ErrOutOfBounds
	}
	return m.numDaysUnchecked(year), nil
}