New aacs::segment_key: parses the AACS 2.1 SegmentKeyNNNNN.tbl container, confirmed against a retail disc as an 8-byte header + 65536 records of 536 bytes, indexed by the 16-bit variant selector the Media Key Variant chain produces. This is the confirmed link between the two 2.1 variant layers (selector picks the device's per-segment variant). The per-record 528-byte payload layout is not yet reversed.
