mux: fix DVD subtitle/audio track collision, PGS/VobSub flush, unify TS codec table

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.

src/disc/bluray.rs

@@ -156,8 +156,16 @@ impl Disc {
                         qualifier: crate::disc::LabelQualifier::None,
                         codec_data: None,
                     })),
-                    // Stream type 4 = IG, unknown types -- skip
-                    _ => None,
+                    // Stream type 4 = IG, unknown types -- skip.
+                    other => {
+                        tracing::warn!(
+                            "dropping STN stream entry: unhandled stream_type {} (PID {:#06x}, coding_type {:#04x})",
+                            other,
+                            s.pid,
+                            s.coding_type,
+                        );
+                        None
+                    }
                 }
             })
             .collect();