Rollup merge of #100819 - WaffleLapkin:use_ptr_byte_methods, r=scottmcm

Make use of `[wrapping_]byte_{add,sub}`

These new methods trivially replace old `.cast().wrapping_offset().cast()` & similar code.
Note that [`arith_offset`](https://doc.rust-lang.org/std/intrinsics/fn.arith_offset.html) and `wrapping_offset` are the same thing.

r? ``@scottmcm``

_split off from #100746_

library/std/src/lib.rs

@@ -300,6 +300,7 @@
 #![feature(panic_can_unwind)]
 #![feature(panic_info_message)]
 #![feature(panic_internals)]
+#![feature(pointer_byte_offsets)]
 #![feature(pointer_is_aligned)]
 #![feature(portable_simd)]
 #![feature(prelude_2024)]