Harden mux + decrypt paths; fail-loud on unresolvable keys

mp4 demuxer (untrusted input): bound every allocation sized from a box
field (stsz/stco/stsc counts, stts/ctts run-lengths, per-sample and moov
sizes, plus an absolute cap so a sparse file can't inflate file_len);
guard the parse_stsd slice and a zero mdhd timescale; cap track count so
the per-track PID can't overflow; rewrite read_moov to handle size==0 /
size<8 / 64-bit largesize; parse esds/AudioSpecificConfig for AAC; write
tkhd duration in the movie timescale.

decrypt: resolve_mux_key_map now fails loud on an extent no key can
classify instead of inheriting the previous extent's key, so a keymap
never silently carries a wrong key; the sweep/patch key-fetch recovery
fails loud when a unit is still unresolved after the retry.

AACS: reject inverted forensic segments in both range builders; compare
the forensic index in u16 space so an out-of-range value can't truncate
onto a valid u8 index. RECOVERED_ERROR no longer latches the damage zone,
preserving the 30s wedge cooldown for a following hard error.

audio: AAC/MP2/MP3/FLAC carry the last PTS across a PES with no timestamp;
the DTS-HD extension-sync search is bounded to after the core; the MP4
16.16 sample-rate field saturates. demux_sink records the video reference
before the kind filter so audio:// / sub:// keep multi-clip PTS continuity
and the DELAY tag.

Remove a dead error variant and the AACS-unsupported-video code; codec
comments cite the primary format specs; assorted doc/naming fixes and
regression tests throughout.

src/mux/resync.rs

@@ -5,9 +5,9 @@
 //! When packets are lost, the affected access unit is already dropped at the TS
 //! layer (the assembler drops the partial PES on the continuity gap). But for
 //! INTER-CODED video the frames that follow reference the lost frame (and each
-//! other) until the next IRAP/IDR keyframe — emitting them yields an ffmpeg
-//! "missing reference / non-existing PPS" deep-scan error and visibly broken
-//! decode. So after a gap on a video track we DROP FORWARD to the next keyframe
+//! other) until the next IRAP/IDR keyframe — emitting them makes any decoder
+//! fault on the "missing reference / non-existing PPS" condition and visibly
+//! break decode. So after a gap on a video track we DROP FORWARD to the keyframe
 //! and resume cleanly there. The gap rounds up to (at most) one GOP — the price
 //! of never emitting a dangling reference; it is logged.
 //!