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/aacs/crypto.rs

@@ -49,7 +49,7 @@ pub(crate) fn aes_ecb_decrypt(key: &[u8; 16], data: &[u8; 16]) -> [u8; 16] {
 /// expansions.
 pub(crate) fn aes_cbc_encrypt(key: &[u8; 16], data: &mut [u8]) {
     debug_assert!(
-        data.len() % 16 == 0,
+        data.len().is_multiple_of(16),
         "aes_cbc_encrypt requires a block-aligned slice"
     );
     let cipher = Aes128::new(GenericArray::from_slice(key));
@@ -71,7 +71,7 @@ pub(crate) fn aes_cbc_encrypt(key: &[u8; 16], data: &mut [u8]) {
 
 pub(crate) fn aes_cbc_decrypt(key: &[u8; 16], data: &mut [u8]) {
     debug_assert!(
-        data.len() % 16 == 0,
+        data.len().is_multiple_of(16),
         "aes_cbc_decrypt requires a block-aligned slice"
     );
     let cipher = Aes128::new(GenericArray::from_slice(key));