[Feature Request] `BufferIterator` should have implemented `Send` and `Sync`

### Problem or motivation

 Just like `std::vec::IntoIter`. Because why not?

### Proposed solution

```rust
unsafe impl<T: Send> Send for BufferIterator<T> {}
unsafe impl<T: Sync> Sync for BufferIterator<T> {}
```

### Additional context

_No response_