Function spawn_fifo_blocking 

pub async fn spawn_fifo_blocking<R: Send + 'static>(
    f: impl FnOnce() -> R + Send + 'static,
    operation: &'static str,
) -> Result<R, SpawnError>

Spawn a blocking function on the Rayon thread pool (FIFO scheduling).

Uses FIFO scheduling which prevents starvation of older tasks. This is the preferred variant for packet decoding and similar ordered workloads.

Includes cooperative cancellation: if the receiver is dropped before the task starts (e.g., timeout), the task is skipped without executing.

Errors

Returns SpawnError::QueueFull if the outstanding task count exceeds the limit.