Changes

• Add bstream::channel_with_notifier() for notification-invalidated sender readiness. Watermark and terminal-state transitions, including receiver drop, invalidate subscribed services before waking waiters. Putting data back also updates sender backpressure. Plain channels do not allocate a notifier.

• KeepAliveService invalidates cached readiness when its idle timer expires. Its callback timer is canceled on shutdown or drop and rearms extended deadlines without waking readiness. Calls extend the deadline, and an explicit readiness bypass can restart an expired service.

• BufferService preserves queue/token cleanup when readiness callbacks panic and invalidates capacity before waking requests canceled during shutdown.

• InFlightService and OneRequestService notify readiness changes when capacity fills or is released, including on cancellation and errors. Notifications reach every pipeline sharing the service. Counter::bind() subscribes other services to the counter's capacity changes.

• Both limiters keep an independent readiness cache for the wrapped service. Capacity notifications preserve that cache; wrapped services must notify their own readiness changes. InFlightService no longer uses call_nowait().

• Add local time::CallbackTimer with reusable one-shot callbacks, reset, cancellation and shutdown-safe delivery

• Restore timer wheel storage on unwinding. Wakers run in place without a notification buffer and must not reenter the timer wheel. Callback delivery runs outside wheel access and refreshes time before processing further timers