Function run_notifier 

pub async fn run_notifier<T, F, Fut>(
    receiver: Receiver<T>,
    max_concurrent_notifications: NonZeroUsize,
    handler: F,
)
where
    F: FnMut(T) -> Fut,
    Fut: Future<Output = ()>,

Delivers queued notifications with bounded concurrency.

The caller schedules this future on its runtime. Closing all senders drains queued and in-flight notifications. Handler failures are handled by the caller; this worker does not retry or propagate them into write completion.