Rust 1.81.0 clippy fixes

Summary:
The Rust toolchain was just updated to 1.81.0 in D63864870. This diff
fixes the newly surfaced rust/clippy lints in rust_foundation owned
code.

Reviewed By: VladimirMakaev

Differential Revision: D64024076

fbshipit-source-id: ed284a9c627fee3e12f858ddd815c8a4a1bd031f

shed/memcache_stub/common/keygen.rs

@@ -22,7 +22,7 @@ impl KeyGen {
         C: AsRef<str>,
     {
         let category = category.as_ref();
-        let all_ascii = category.chars().all(|c| c.is_ascii());
+        let all_ascii = category.is_ascii();
         let no_bad = !category.chars().any(|c| c == ' ' || c == ':');
 
         assert!(all_ascii, "category is not pure ascii");