pub(crate) fn map_key_bound(bound: Bound<KeySlice>) -> Bound<KeyBytes> {
    match bound {
        Bound::Included(x) => Bound::Included(KeyBytes::from_bytes_with_ts(
            Bytes::copy_from_slice(x.key_ref()),
            x.ts(),
        )),
        Bound::Excluded(x) => Bound::Excluded(KeyBytes::from_bytes_with_ts(
            Bytes::copy_from_slice(x.key_ref()),
            x.ts(),
        )),
        Bound::Unbounded => Bound::Unbounded,
    }
}
Create a bound of `Bytes` from a bound of `KeySlice`.
mini-lsm-mvcc/src/mem_table.rs