SegmentKey is used to index segment data, where keys a lexicographically ordered.
The scheme is {u64::MAX - start_frame_no}-{u64::MAX - end_frame_no}. With that naming convention, when looking for
the segment containing ‘n’, we can perform a prefix search with “{u64::MAX - n}”. The first
element of the range will be the biggest segment that contains n if it exists.
Beware that if no segments contain n, either the smallest segment not containing n, if n < argmin
{start_frame_no}, or the largest segment if n > argmax {end_frame_no} will be returned.
e.g: