Chapters, DVD subtitle palette, MKV track flags, progress total_bytes

Chapters:
- MPLS PlayList marks parsed (mark_type 1 = chapter)
- Chapter struct on DiscTitle (time_secs, name)
- MKV Chapters element with EditionEntry/ChapterAtom per mark
- 3 MPLS mark tests + 2 MKV chapter tests

DVD subtitle palette:
- IFO palette extraction (PGC offset 0xA4, 16 × YCbCr colors)
- YCbCr→RGB conversion for VobSub .idx format
- DvdSubParser codec_private returns formatted palette
- codec_data field on SubtitleStream flows through pipeline
- 5 palette tests (YCbCr conversion, formatting, overflow)

MKV track flags:
- FlagDefault: primary video/audio = 1, secondary = 0
- FlagForced: forced subtitles = 1
- Language: set from stream language code
- Already implemented, verified with 4 new tests

Progress total_bytes:
- IOStream trait: total_bytes() -> Option<u64>
- DiscStream, IsoStream: from disc_title.size_bytes
- M2tsStream, MkvStream: from file metadata on open
- NetworkStream, StdioStream, NullStream: None

316 tests total, all passing.

src/mux/meta.rs

@@ -168,6 +168,7 @@ impl M2tsMeta {
                     codec: str_to_codec(codec),
                     language: language.clone(),
                     forced: *forced,
+                    codec_data: None,
                 }),
             })
             .collect();
@@ -179,6 +180,7 @@ impl M2tsMeta {
             size_bytes: 0,
             clips: Vec::new(),
             streams,
+            chapters: Vec::new(),
             extents: Vec::new(),
             content_format: crate::disc::ContentFormat::BdTs,
         }