Add missing Debug derive to vec::IntoIter

[zeenix]

No description provided.

[sosthene-nitrokey]

This would lead to undefined behaviour.

The vec field in the IntoIter struct is not in a valid state after iteration has begun. All elements before next have been "removed" from the Vec through unsafe code even though it's still there. All methods on IntoIter must take care to not read from them.

If you want a Debug implementation, you will need not to go through derive, but instead write a manual implementation. You can take a look at the Clone implementation to see how Debug could be implemented manually.

[sosthene-nitrokey]

This is where Unsafe fields could come in handy in the future.

[zeenix]

@sosthene-nitrokey Thanks for the review. PTALA. I was first going for a more verbose option (f.debug_struct("IntoIter").field("elements", &s).finish()) but then decided against it. I can change to something like that, if you like.