Function parallel_batch_process 

pub fn parallel_batch_process<T, R, F>(
    items: &[T],
    batch_size: usize,
    processor: F,
) -> Result<Vec<R>>
where
    T: Sync,
    R: Send,
    F: Fn(&[T]) -> Result<Vec<R>> + Sync + Send,

Parallel batch processing with configurable thread pool