Write a ShardedSigDb: one shared dictionary file, one blob-only file per shard, and a SigDbManifest
that embeds each shard's index and references the shared dictionary by id; needs no .idx sidecars. With pack,
also assembles a clean copy-into-flowR folder.
Write a ShardedSigDb: one shared dictionary file, one blob-only file per shard, and a SigDbManifest that embeds each shard's index and references the shared dictionary by id; needs no
.idxsidecars. Withpack, also assembles a clean copy-into-flowR folder.