Use fill_bytes_via_u32 in JitterRng

src/jitter.rs

@@ -738,7 +738,13 @@ impl Rng for JitterRng {
     }
 
     fn fill_bytes(&mut self, dest: &mut [u8]) {
-        impls::fill_bytes_via_u64(self, dest)
+        // Fill using `next_u32`. This is faster for filling small slices (four
+        // bytes or less), while the overhead is negligible (in benchmarks even
+        // slightly faster instead of slower).
+        //
+        // This is done especially for wrappers that implement `next_u32`
+        // themselves via `fill_bytes`.
+        impls::fill_bytes_via_u32(self, dest)
     }
 }