DVD vob_start absolute rebase + rc.5.3 audit fixes

- ifo.rs: rebase VTS title VOBS to absolute disc LBA (file_start_lba +
  vtstt_vobs); fixes DVD rips opening on the menu region instead of the
  movie (e.g. SOTL). Adds absolute-placement regression test.
- aacs/boil.rs: add mk_from_pk primitive (PK -> MK via MKB walk).
- dvdnav/: nav-VM command decoder + start-cell resolver seam, parked
  behind USE_NAV_RESOLVER (kept compiled, never executed).
- mux: FVI src.byte within-sector per spec; Unknown colour -> CICP
  unspecified (2,2,2,1); demux clear PCS -> NORMAL; ts.rs feed() base
  reset + boundary provenance fix.
- Assorted audit fixes (doc/comment/test accuracy) across the crate.

src/mux/codec/hevc.rs

@@ -56,10 +56,7 @@ fn hevc_num_extra_slice_header_bits(pps_nal: &[u8]) -> Option<u32> {
     br.read_ue()?; // pps_pic_parameter_set_id
     br.read_ue()?; // pps_seq_parameter_set_id
     br.skip_bits(2)?; // dependent_slice_segments_enabled_flag, output_flag_present_flag
-    let mut n = 0u32;
-    for _ in 0..3 {
-        n = (n << 1) | br.read_bit()?;
-    }
+    let n = br.read_bits(3)?;
     Some(n)
 }