misc: use prelude size_of

size_of is part of std::prelude as of Rust 1.80 (with size_of_val,
align_of, align_of_val), and the workspace MSRV is 1.89, so qualifying
it (mem::size_of, std::mem::size_of, core::mem::size_of) is unnecessary.

Convert every qualified size_of call-site to the bare prelude form and
drop the now-redundant `use std::mem::size_of;` imports, keeping
`use std::mem;` where it still serves non-prelude items (transmute,
swap, replace, take, zeroed, MaybeUninit, offset_of). size_of is the
only one of the four currently used in the tree.

Pure refactor, no behavioural change. Follow-up to the
clippy::absolute_paths cleanup (#7670), as discussed in #8444.

Signed-off-by: Henry Hrvoje Tonkovac <htonkovac@gmail.com>
Assisted-by: Claude:Opus-4.8

hypervisor/src/lib.rs

@@ -116,7 +116,6 @@ fn vec_with_size_in_bytes<T: Default>(size_in_bytes: usize) -> Vec<T> {
 // for `Foo`, a `Vec<Foo>` is created. Only the first element of `Vec<Foo>` would actually be used
 // as a `Foo`. The remaining memory in the `Vec<Foo>` is for `entries`, which must be contiguous
 // with `Foo`. This function is used to make the `Vec<Foo>` with enough space for `count` entries.
-use std::mem::size_of;
 pub fn vec_with_array_field<T: Default, F>(count: usize) -> Vec<T> {
     let element_space = count * size_of::<F>();
     let vec_size_bytes = size_of::<T>() + element_space;