removeFiber

    fn removeFiber(group: Group, ev: *Evented, fiber: *Fiber) ?*Fiber {
        group.lock(ev);
        defer group.unlock(ev);
        const list_ptr = group.listPtr();
        const list = @atomicLoad(List, list_ptr, .monotonic);
        if (fiber.link.group.next) |next| next.link.group.prev = fiber.link.group.prev;
        if (fiber.link.group.prev) |prev| {
            prev.link.group.next = fiber.link.group.next;
        } else if (fiber.link.group.next) |new_head| {
            @atomicStore(List, list_ptr, .{
                .cancel_requested = list.cancel_requested,
                .awaiter_delayed = list.awaiter_delayed,
                .fibers = .pack(new_head),
            }, .monotonic);
        } else if (@atomicLoad(Awaiter, group.awaiterPtr(), .monotonic).awaiter.unpack()) |awaiter| {
            if (!awaiter.cancel_status.changeAwaiting(.group, .nothing) or list.cancel_requested) {
                @atomicStore(List, list_ptr, .{
                    .cancel_requested = false,
                    .awaiter_delayed = false,
                    .fibers = .null,
                }, .release);
                assert(awaiter.awaiting_group.ptr == group.ptr);
                awaiter.awaiting_group = undefined;
                return awaiter;
            }
            // Race with `Fiber.requestCancel`
            @atomicStore(List, list_ptr, .{
                .cancel_requested = false,
                .awaiter_delayed = true,
                .fibers = .null,
            }, .monotonic);
        } else @atomicStore(List, list_ptr, .{
            .cancel_requested = false,
            .awaiter_delayed = false,
            .fibers = .null,
        }, .release);
        return null;
    }