review: group timedOut with the other wg-published field writes

Address a review note worrying that states[idx].timedOut might not be covered by the wait-group happens-before. It already was (it is written before the deferred wg.Done(), like waitErr/finishedAt, and the main goroutine reads all fields only after wg.Wait() -> close(fanIn) -> the dispatch loop ends). Move the timedOut write up next to waitErr (before finishedAt and before the fanIn sends) and expand the comment to make the wg-based publication explicit. No behavior change; 'go test -race' on the package is clean.