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/bdmt.rs

@@ -100,10 +100,10 @@ pub fn parse(reader: &mut dyn SectorSource, udf: &UdfFs) -> Option<DiscMetadata>
         // Disc-set position is disc-global; first one we successfully
         // read wins. (All bdmt_*.xml on a given disc carry the same
         // value in practice.)
-        if out.disc_number.is_none() {
-            if let Some(ds) = disc_set {
-                out.disc_number = Some(ds);
-            }
+        if out.disc_number.is_none()
+            && let Some(ds) = disc_set
+        {
+            out.disc_number = Some(ds);
         }
     }
 
@@ -184,20 +184,20 @@ fn extract_title(xml_text: &str) -> Option<String> {
     // xml::text already trims its result, so an empty string after
     // extraction means a genuinely empty element.
     for tag in ["name", "title"] {
-        if let Some(s) = xml::text(xml_text, tag) {
-            if !s.is_empty() {
-                return Some(s);
-            }
+        if let Some(s) = xml::text(xml_text, tag)
+            && !s.is_empty()
+        {
+            return Some(s);
         }
     }
     // tableOfContents/titleName: search inside the toc block so we
     // don't accidentally pick a stray <titleName> from elsewhere.
     if let Some((s, e)) = xml::find_element(xml_text, "tableOfContents", 0) {
         let block = &xml_text[s..e];
-        if let Some(t) = xml::text(block, "titleName") {
-            if !t.is_empty() {
-                return Some(t);
-            }
+        if let Some(t) = xml::text(block, "titleName")
+            && !t.is_empty()
+        {
+            return Some(t);
         }
     }
     None