With the EL now carried (mpls PID fix), the MKV writer tags the Dolby
Vision layer so players/mediainfo recognise it: a BlockAdditionMapping
(0x41E4) with BlockAddIDType 'dvcC' and a DOVIDecoderConfigurationRecord
(profile 7, bl+el+rpu present) on the DV-layer video track. Disc
Profile 7 dual-layer is preserved losslessly as a second video track
(archival-correct, MakeMKV-equivalent); M2TS carries the EL as a native
second video PID with no extra signaling needed.
Adds dolby_vision_config() + a profile-7 dvcC unit test. End-to-end DV
recognition (mediainfo / playback) to be confirmed on a full rip.