Sweep the pinned toolchain to Rust 1.97

The Windows UI needs current winsafe, whose real minimum is 1.89 (its manifest
under-declares 1.87 while it uses NonNull::from_ref). Rather than stop at the
minimum, this goes to current stable and fixes what that costs.

The counter-intuitive result: 1.97 is CHEAPER than 1.89. libfreemkv had 54
clippy errors at 1.89 and 6 at 1.97, because clippy tightened the noisy
collapsible_if lint in between. Stopping at the minimum would have been the most
expensive choice available.

Roughly 47 lints across the eight repos, the large majority auto-fixed:
libfreemkv 6, freemkv-engine 14, bdemu 8, freemkv-keysources 7, autorip 6,
freemkv-unlock 3, freemkv-i18n 3. The hand-fixed ones are a descending sort to
sort_by_key(Reverse), four manual checked-division sites, a loop counter replaced
by enumerate, and a loop whose first let-else became a while-let.

Worth recording for whoever bumps next: clippy is MSRV-AWARE. Those 54 lints only
appear once the crate DECLARES 1.89 or later, because let-chains become
available. A bare `cargo +1.89 clippy` against a manifest still pinned at 1.87
reports clean and is meaningless — gate with the real precommit script, which is
also the only thing that covers build scripts.

The pin still sits below the Mac default, so it keeps doing its job: catching
lint drift locally before CI sees it.

src/disc/pgs_forced_probe.rs

@@ -42,7 +42,7 @@ const CHUNK_SECTORS: u16 = 1023;
 
 // The alignment requirement above is enforced, not just described.
 const _: () = assert!(
-    CHUNK_SECTORS as u32 % crate::aacs::content::ALIGNED_UNIT_SECTORS == 0,
+    (CHUNK_SECTORS as u32).is_multiple_of(crate::aacs::content::ALIGNED_UNIT_SECTORS),
     "probe chunks must be a whole number of AACS aligned units"
 );
 
@@ -393,12 +393,11 @@ fn verdicts(evidence: &HashMap<u16, TrackEvidence>, conclusive: bool) -> HashMap
 /// from the map was never observed and keeps its vendor-derived flag.
 fn apply_verdicts(title: &mut DiscTitle, verdicts: &HashMap<u16, bool>) {
     for s in &mut title.streams {
-        if let Stream::Subtitle(sub) = s {
-            if sub.codec == Codec::Pgs {
-                if let Some(&forced) = verdicts.get(&sub.pid) {
-                    sub.forced = forced;
-                }
-            }
+        if let Stream::Subtitle(sub) = s
+            && sub.codec == Codec::Pgs
+            && let Some(&forced) = verdicts.get(&sub.pid)
+        {
+            sub.forced = forced;
         }
     }
 }