Subtitle/DVD output-corruption + stream-mapping coverage fixes.
1. DVD subtitle/audio track-mapping collision (CRITICAL). The PS path
routed 0xBD private-stream packets to a track via (sub_id & 0x1F)+1,
so VobSub subtitle sub-id 0x20+j aliased audio track j+1: subtitle
PES was fed to the AC-3 parser and the real subtitle track got
nothing. Route by the canonical DVD PID instead via a new
PsPacket::dvd_pid() that mirrors scan_dvd_titles' PID assignment
(video 0xE0, audio 0xBD00+i, subtitle 0x20+j), then look up the
track in pid_to_track. Fixed identically at all three sites
(pipelined_stream consume_ps, disc.rs live feed, disc.rs EOF flush).
Unmappable/unmapped packets now WARN instead of silently dropping.
2. PGS flush() missing. PgsParser inherited the no-op default flush, so
the last subtitle of every PGS track (emitted only when a following
PCS arrives) was dropped at EOF. Implemented flush() to drain the
pending display set (duration_ns: None for the trailing block).
3. DVD VobSub multi-PES SPU not reassembled. A subpicture unit larger
than one PES spans multiple PES (only the head carries a PTS).
DvdSubParser is now stateful: it buffers per sub-stream until the
leading 2-byte SPU_size is satisfied, inherits the head PTS, and
emits one Frame. flush() drains a truncated trailing SPU at EOF.
4. One-table hygiene. scan_streams had a duplicate stream_type->Codec
table that had drifted from Codec::from_coding_type (missing 0x80
LPCM, 0x85 mapped to DTS-HD MA vs HR, etc.). scan_streams now uses
from_coding_type plus a new Codec::kind()/CodecKind category split,
so the two mappings can never diverge. Silent drops in
scan_streams and bluray STN parsing now WARN with PID + type.
Tests: dvd_pid mapping + subtitle/audio collision regression, PGS
final-subtitle flush, VobSub multi-PES reassembly + EOF flush,
scan_streams 0x80 LPCM via from_coding_type.
MattJackson
cfc12774f2