Auto merge of #96711 - emilio:inline-slice-clone, r=nikic

Auto merge of #96711 - emilio:inline-slice-clone, r=nikic

slice: #[inline] a couple iterator methods.

The one I care about and actually saw in the wild not getting inlined is
clone(). We ended up doing a whole function call for something that just
copies two pointers.

I ended up marking as_slice / as_ref as well because make_slice is
inline(always) itself, and is also the kind of think that can kill
performance in hot loops if you expect it to get inlined. But happy to
undo those.