A single impl supports all of `[T]`, `Vec<T>` and `CVec<T>`. Once `Iterable` is implemented, we will prefer it to `SlicePrelude`. But the `with_capacity()` part might become tricky.
A single impl supports all of `[T]`, `Vec<T>` and `CVec<T>`. Once `Iterable` is implemented, we will prefer it to `SlicePrelude`. But the `with_capacity()` part might become tricky.