Class AsyncPollingProxyTransfer<T>

Duplex transfer with asynchronous polling that receives its fetcher from the previous node.

Capabilities: isInput, isOutput, isDuplex, isAsyncPollingProxy, isPollingSource, isAsyncPullable, isSubscribable, isAsyncTriggerable, isGate

Mechanics:

1. The constructor accepts config (interval, activated), but NOT a fetcher
2. setAsyncFetcher(fetcher) — sets the async fetcher, creates a Ticker, starts if active
3. clearAsyncFetcher() — stops the Ticker, clears the fetcher
4. asyncTrigger() — calls await fetcher(), notifies subscribers (if active)
5. asyncPull() — calls await fetcher() directly (if active and fetcher is set)
6. The _polling flag prevents overlapping
7. activate()/deactivate()/toggle() — control polling

Error handling:

• If fetcher() throws an exception, onError is called.
• With onError provided, the exception is suppressed. Without onError — rethrown.
• The 'Async fetcher is not defined' error is always rethrown.
• When the ticker fires asyncTrigger() without onError, the rejection is unhandled (visible in logs as unhandled promise rejection). To suppress — provide onError.

Configuration (AsyncPollingProxyTransferConfig):

• interval: number — polling interval (ms)
• activated: boolean — initial polling state
• tickerFactory?: TickerFactory
• onError?: ErrorHandler