audit: bound DTS marks, align disc-format tree order, doc/test cleanups

Round-7 findings from the 10-phase release audit (no HIGH; convergence):

- Cap DtsParser.pts_marks (MAX_PTS_MARKS): a run of zero-length timed PES
  packets grew no buffer bytes, so the drain_front mark-prune never ran —
  the deque could accumulate without bound on hostile PS input.
- detect_disc_format tested HVDVD_TS before BDMV while the title-scan
  dispatch tests BDMV first, so a disc with both trees would be classified
  HD-DVD but enumerated as Blu-ray. Align both to BDMV → HVDVD_TS →
  VIDEO_TS.
- Document why the DTS new-PES re-base can emit a locally-decreasing PTS
  (the muxer's block_ts applies the strictly-monotonic audio nudge, tested
  in mkv.rs) — this is by design, not a mux defect.
- Fix stale aacs/keys.rs comment references (functions moved to
  aacs/inf.rs / aacs::resolve/derive in the module split).

src/disc/mod.rs

@@ -2129,12 +2129,9 @@ impl Disc {
         titles: &[DiscTitle],
     ) -> DiscFormat {
         use crate::aacs::mkb::{AacsVersion, mkb_type};
-        if udf_fs.find_dir("/HVDVD_TS").is_some() {
-            return DiscFormat::HdDvd;
-        }
-        if udf_fs.find_dir("/VIDEO_TS").is_some() {
-            return DiscFormat::Dvd;
-        }
+        // Tree priority MUST match the title-scan dispatch (BDMV → HVDVD_TS →
+        // VIDEO_TS): otherwise a disc carrying two trees would be classified as
+        // one format but enumerated as another (e.g. BD titles tagged HdDvd).
         if udf_fs.find_dir("/BDMV").is_some() {
             // Only the Type-and-Version record (first record) is needed.
             if let Ok(mkb) = udf_fs.read_file_prefix(reader, "/AACS/MKB_RO.inf", 64) {
@@ -2151,6 +2148,12 @@ impl Disc {
                 other => other,
             };
         }
+        if udf_fs.find_dir("/HVDVD_TS").is_some() {
+            return DiscFormat::HdDvd;
+        }
+        if udf_fs.find_dir("/VIDEO_TS").is_some() {
+            return DiscFormat::Dvd;
+        }
         DiscFormat::Unknown
     }