Function parallel_scan 

pub fn parallel_scan<T, F>(items: &[T], init: T, op: F) -> Vec<T>
where
    T: Clone + Send + Sync,
    F: Fn(&T, &T) -> T + Sync,

Parallel scan (prefix sum) operation

Computes cumulative operation (like cumulative sum) in parallel. Returns a vector where each element is the result of applying the operation to all preceding elements including itself.