Add DiscFormat::Fmts (AACS 2.1) and DiscFormat::HdDvd as first-class peers. Format derives from the AACS MKB generation (mkb_type().generation(): V10=BD, V20=UHD, V21=FMTS), reusing existing AACS code, and from the on-disc tree for HD-DVD/DVD. One detector (detect_disc_format) shared by the coarse DiscId probe and the full scan — no more 'default BluRay, defer to full scan'.
FMTS is a BD-tree stream variant: parse_playlist resolves the clip stream via CLIP_STREAM_EXTS (.m2ts -> .fmts -> .ssif), so the .fmts main feature yields real extents (previously silently empty). HD-DVD is a tree-level peer with its own enumerator (disc/hddvd.rs): HVDVD_TS/*.evo -> MpegPs titles with real extents (playlist/stream parsing honestly stubbed).
Sample selection for key resolution now uses the authoritative AACS CPI flag (aacs_unit_encrypted, byte-0 & 0xC0) not the ts_sync_destroyed heuristic — container-agnostic (M2TS/FMTS/EVO; TS-sync is meaningless on HD-DVD program streams) and stops the decode-server '0 encrypted units' rejection.
Tests live with each format (bluray/hddvd/mod); generic UDF fixture builders extracted to a shared udf::fixture module.
Matthew Jackson
85347597cc