Default Ankusa.Codec: length-prefixed, CRC-checked framing with no
compression.
Each record is framed as:
<<len::32, crc32::32, payload::binary>>where crc32 = :erlang.crc32(payload) covers the payload only. encode/1
concatenates the frames into one segment binary and returns a per-record index
of {key, offset, length} — offset is the frame start byte within the
segment and length is the full frame length (payload plus the 8-byte header),
exactly the byte range Ankusa.BlobStore.get_range/5 must fetch for
decode_record/1. The offsets are relative to the first frame; the segment
header (Ankusa.Storage.Segment) shifts them when it wraps the frames.