Use size_of from the prelude instead of imported

Use `std::mem::{size_of, size_of_val, align_of, align_of_val}` from the
prelude instead of importing or qualifying them.

These functions were added to all preludes in Rust 1.80.

crates/test-utils/src/minicore.rs

@@ -1825,7 +1825,7 @@ macro_rules! impl_int {
     ($($t:ty)*) => {
         $(
             impl $t {
-                pub const fn from_ne_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
+                pub const fn from_ne_bytes(bytes: [u8; size_of::<Self>()]) -> Self {
                     unsafe { mem::transmute(bytes) }
                 }
             }