This method converts the current iterator into an iterator that will yield only the leaves of the tree. Iteration still proceeds in either a breadth first search (if called on a breadth first iterator) or depth first post-order search (if called on a depth first pre-, in-, or post-order iterator). This method is safe to call at any point during iteration and will never panic.

A leaf is defined as: Any tree node that has no children. Given a tree of the following shape, this iterator would always yield values in the following order (regardless of iteration type, but this is not always the case):
\[0, 1, 3\], \[0, 1, 4\], \[0, 2, 5\], \[0, 2, 6, 7, 8, 9, 10\]

```ignore
       0
      / \
     1   2
    / \ / \
   3  4 5  6
          /
         7
          \
           8
          /
         9
          \
          10
```

```rust
// Example usage:
use streaming_iterator::StreamingIterator;
use tree_iterators_rs::{
    prelude::*,
    examples::create_example_binary_tree
};

let root = create_example_binary_tree();
let mut leaves_streaming_iter = root.dfs_postorder().attach_ancestors().leaves();
while let Some(leaf_with_ancestors) = leaves_streaming_iter.next() {
    println!("{:?}", leaf_with_ancestors);
}
```