Function run_with_concurrency_limit 

pub async fn run_with_concurrency_limit<T, O, F, Fut>(
    items: Vec<T>,
    limit: usize,
    handler: F,
) -> Vec<O>
where
    F: FnMut(T) -> Fut,
    Fut: Future<Output = O>,

Runs item handlers with a bounded number of in-flight futures.

Claimed task batches are already capacity-checked by lane claiming. This helper only preserves the product’s requested upper bound while letting independent task futures finish out of order.