cancelThreads

    fn cancelThreads(g: Group, t: *Threaded) bool {
        var any_blocked = false;
        var it = t.worker_threads.load(.acquire); // acquire `Thread` values
        while (it) |thread| : (it = thread.next) {
            // This non-mutating RMW exists for ordering reasons: see comment in `Group.Task.start` for reasons.
            _ = thread.status.fetchOr(.{ .cancelation = @fromBackingInt(@intCast(0)), .awaitable = .null }, .release);
            if (thread.cancelAwaitable(.fromGroup(g.ptr))) any_blocked = true;
        }
        return any_blocked;
    }