Serialise a columnar index (M7) to a sidecar blob — same format as
serializeIndexSidecar, byte for byte, but read straight off the SoA
columns so no object index is needed. Only the top-level range is carried
(the v1 format; inline rows re-materialise from record bytes on demand).
Serialise a columnar index (M7) to a sidecar blob — same format as serializeIndexSidecar, byte for byte, but read straight off the SoA columns so no object index is needed. Only the top-level range is carried (the v1 format; inline rows re-materialise from record bytes on demand).