pub fn block_on_multi<F>(future: F, num_workers: usize) -> F::OutputExpand description
Drive future to completion using num_workers OS threads.
Worker 0 is the main thread (drives root future). Workers 1..N-1 are spawned as background threads. All workers share GlobalQueue and steal tasks.
When num_workers <= 1, falls back to block_on_with_spawn (single-thread).