libfreemkv: rc.5.1 DVD correctness fixes

- CSS: unlock scrambled-sector reads on enforcing drives via bus-auth
  only; classify sense 6F/03 as CSS-locked; early-bail on a fully locked
  scan; gate the AACS handshake off DVD discs.
- DVD first-play menu no longer prepended to the feature: read the title
  VOBS base from vtstt_vobs (0xC4), not the menu VOBS vtsm_vobs (0xC0).
- Interlaced field-duration (DefaultDecodedFieldDuration) written as a
  direct TrackEntry child rather than inside Video, so Windows reports
  the correct frame rate.
- Audio channel count read from the AC-3 bitstream; FieldOrder set to
  TFF; per-track BPS tags.
- Structured disc diagnostics at --log-level 3; reduced per-operation
  log spam.

src/drive/mod.rs

@@ -370,7 +370,7 @@ impl Drive {
     }
 
     /// True when the mounted disc is a DVD (profile family `0x0010..=0x001F`).
-    fn disc_is_dvd(&mut self) -> bool {
+    pub(crate) fn disc_is_dvd(&mut self) -> bool {
         matches!(self.current_profile(), Some(p) if (0x0010..=0x001F).contains(&p))
     }