0.31.0: hardening and correctness pass across mux, codec, AACS/CSS, UDF/MPLS/CLPI, recovery, drive/SCSI, labels, and I/O

Library-wide review-and-fix pass: tightened AACS keydb/handshake/variant
handling and trailing-partial-unit policy, corrected MPLS mark offset and
added UDF allocation bounds, hardened the mux/codec framing and M2TS paths,
guarded SCSI READ CAPACITY short transfers and unified error mapping, added
overflow guards on untrusted disc input, and made prefetch shutdown
deterministic. Release profile now builds with thin LTO + single codegen unit.

src/halt.rs

@@ -34,11 +34,9 @@ impl Halt {
         Self(Arc::new(AtomicBool::new(false)))
     }
 
-    /// Wrap an existing `Arc<AtomicBool>` as a `Halt`. Useful as a
-    /// bridge during the 0.18 deprecation window: callers that already
-    /// hold an `Arc<AtomicBool>` (e.g. `Drive::halt_flag()`, the
-    /// deprecated `DiscStream::set_halt`) can adopt the new token API
-    /// without changing the underlying flag.
+    /// Wrap an existing `Arc<AtomicBool>` as a `Halt`. A bridge for
+    /// callers that already hold an `Arc<AtomicBool>` cancellation flag
+    /// and want to adopt the token API without allocating a new flag.
     ///
     /// Cancelling either side flips the same bit — the wrapping `Halt`
     /// and the original `Arc` are two views over one shared flag.
@@ -46,10 +44,9 @@ impl Halt {
         Self(flag)
     }
 
-    /// Borrow the underlying `Arc<AtomicBool>`. Used at boundaries with
-    /// pre-`Halt` APIs that still take an `Arc<AtomicBool>` directly
-    /// (`CopyOptions::halt`, the deprecated `DiscStream::set_halt`).
-    /// Round 3 deletes those boundaries and this accessor with them.
+    /// Borrow the underlying `Arc<AtomicBool>`. The inverse of
+    /// [`from_arc`](Self::from_arc): hand the shared flag to an API that
+    /// still takes a raw `Arc<AtomicBool>` rather than a `Halt`.
     pub fn as_arc(&self) -> &Arc<AtomicBool> {
         &self.0
     }