NewErrNoPagesInInterval creates a new instance of ErrNoPagesInInterval.

NewPageInterval creates a new instance of PageInterval with empty intervals and a page count of 0.

PageRangeIterator returns an iterator that iterates over the pages in the interval.

ErrNoPagesInInterval represents an error where there are no pages in the interval.

PageInterval represents a collection of page intervals, where each interval is represented by a pair of integers.