Enable the clippy::std_instead_of_core lint (#8394)

Prefer `core::` over `std::` where either work

* Part of https://github.com/emilk/egui/issues/5735

crates/egui_extras/src/loaders/svg_loader.rs

@@ -1,4 +1,5 @@
-use std::{mem::size_of, sync::Arc};
+use core::mem::size_of;
+use std::sync::Arc;
 
 use ahash::HashMap;