pub(crate) fn map_bound(bound: Bound<&[u8]>) -> Bound<Bytes> {
    match bound {
        Bound::Included(x) => Bound::Included(Bytes::copy_from_slice(x)),
        Bound::Excluded(x) => Bound::Excluded(Bytes::copy_from_slice(x)),
        Bound::Unbounded => Bound::Unbounded,
    }
}
Create a bound of `Bytes` from a bound of `&[u8]`.
mini-lsm/src/mem_table.rs