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/extract.rs

@@ -165,13 +165,13 @@ impl Disc {
             .iter()
             .map(|p| p.size)
             .fold(0u64, |a, b| a.saturating_add(b));
-        if let Some(available) = available_space(dest) {
-            if available < required {
-                return Err(Error::DirInsufficientSpace {
-                    required,
-                    available,
-                });
-            }
+        if let Some(available) = available_space(dest)
+            && available < required
+        {
+            return Err(Error::DirInsufficientSpace {
+                required,
+                available,
+            });
         }
 
         // Create directories up-front so a leaf write never races a missing
@@ -388,12 +388,12 @@ fn plan_tree(
         let child_rel = host_rel.join(&safe);
         let child_disc = format!("{disc_path}/{}", entry.name);
         // Collision: two distinct disc paths → same host path.
-        if let Some(prev) = seen_hosts.insert(child_rel.clone(), child_disc.clone()) {
-            if prev != child_disc {
-                return Err(Error::DirNameCollision {
-                    host: child_rel.to_string_lossy().into_owned(),
-                });
-            }
+        if let Some(prev) = seen_hosts.insert(child_rel.clone(), child_disc.clone())
+            && prev != child_disc
+        {
+            return Err(Error::DirNameCollision {
+                host: child_rel.to_string_lossy().into_owned(),
+            });
         }
         if entry.is_dir {
             dirs.push(child_rel.clone());
@@ -756,10 +756,11 @@ fn is_windows_reserved(base: &str) -> bool {
     }
     let up = base.to_ascii_uppercase();
     for prefix in ["COM", "LPT"] {
-        if let Some(rest) = up.strip_prefix(prefix) {
-            if rest.len() == 1 && matches!(rest.as_bytes()[0], b'1'..=b'9') {
-                return true;
-            }
+        if let Some(rest) = up.strip_prefix(prefix)
+            && rest.len() == 1
+            && matches!(rest.as_bytes()[0], b'1'..=b'9')
+        {
+            return true;
         }
     }
     false