EncodeLike<Vec<T>> should be implemented for Iterators with wrapping structure

Similarly to Ref structure we could introduce 
```rust
struct Iter<I: Iterator<T>, T: Encode>(&I, Phantom<T>)
```
or maybe 
```rust
struct Iter<I: Iterator<T>, T: EncodeLike<U>, U: Encode>(&I, Phantom<(T, U)>)
```

And then implement `EncodeLike<Vec<U>>` for it.