Align `ArrayWindows` trait impls with `Windows` With `slice::ArrayWindows` getting ready to stabilize in 1.94, I noticed that it currently has some differences in trait implementations compared to `slice::Windows`, and I think we should align these. - Remove `derive(Copy)` -- we generally don't want `Copy` for iterators at all, as this is seen as a footgun (e.g. rust-lang/rust#21809). This is obviously a breaking change though, so we should only remove this if we also backport the removal before it's stable. Otherwise, it should at least be replaced by a manual impl without requiring `T: Copy`. - Manually `impl Clone`, simply to avoid requiring `T: Clone`. - `impl FusedIterator`, because it is trivially so. The `since = "1.94.0"` assumes we'll backport this, otherwise we should change that to the "current" placeholder. - `impl TrustedLen`, because we can trust our implementation. - `impl TrustedRandomAccess`, because the required `__iterator_get_unchecked` method is straightforward. r? libs-api @rustbot label beta-nominated (at least for the `Copy` removal, but we could be more selective about the rest).