Function diff_children 

pub fn diff_children(
    old_children: &[Box<dyn ElementBuilder>],
    new_children: &[Box<dyn ElementBuilder>],
) -> Vec<ChildDiff>

Diff children using content-hash-based matching.

This algorithm:

1. Computes hashes for all children
2. Matches children by hash (handles reordering)
3. Detects additions, removals, and modifications