fix: second round of clippy lints

Clippy would not automatically apply these fixes, so they were applied
by hand.

constant-time/src/lib.rs

@@ -16,7 +16,7 @@ use rosenpass_to::{with_destination, To};
 ///
 /// If source and destination are of different sizes.
 #[inline]
-pub fn xor<'a>(src: &'a [u8]) -> impl To<[u8], ()> + 'a {
+pub fn xor(src: &[u8]) -> impl To<[u8], ()> + '_ {
     with_destination(|dst: &mut [u8]| {
         assert!(src.len() == dst.len());
         for (dv, sv) in dst.iter_mut().zip(src.iter()) {