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/labels/mod.rs

@@ -574,10 +574,10 @@ fn extract(reader: &mut dyn SectorSource, udf: &UdfFs) -> Vec<StreamLabel> {
     // so the user sees every track even when only the "interesting"
     // ones have editorial names. Skips the merge when mpls_universal
     // was itself the chosen parser (its labels ARE the labels).
-    if name != "mpls_universal" {
-        if let Some(mpls_result) = mpls_universal::parse(reader, udf) {
-            fill_gaps_from_mpls(&mut labels, &mpls_result.labels);
-        }
+    if name != "mpls_universal"
+        && let Some(mpls_result) = mpls_universal::parse(reader, udf)
+    {
+        fill_gaps_from_mpls(&mut labels, &mpls_result.labels);
     }
 
     // CLPI orphan streams: PIDs in /BDMV/CLIPINF/*.clpi ProgramInfo