Class AsyncPollingSourceTransfer<T>

Output transfer with asynchronous internal polling of a data source.

Capabilities: isOutput, isPollingSource, isAsyncPullable, isSubscribable, isAsyncTriggerable, isGate

Mechanics:

1. The constructor accepts config.fetcher: AsyncDataFetcher
2. An internal Ticker calls asyncTrigger() (fire-and-forget)
3. asyncTrigger() — calls await fetcher(), writes the result, notifies subscribers
4. asyncPull() — calls await fetcher() directly (without writing to state)
5. The _polling flag prevents overlapping calls with a slow fetcher
6. activate()/deactivate()/toggle() — control polling via the ticker

Error handling:

• If fetcher() throws an exception in asyncTrigger() or asyncPull(), onError is called.
• With onError provided, the exception is suppressed (polling continues).
• Without onError, the exception is rethrown from asyncPull()/asyncTrigger().
• When the ticker fires asyncTrigger() without onError, the rejection is unhandled (visible in logs as unhandled promise rejection). To suppress — provide onError.

Configuration (AsyncPollingSourceTransferConfig):

• fetcher: AsyncDataFetcher — async data retrieval function
• interval: number — polling interval (ms)
• activated: boolean — initial polling state
• tickerFactory?: TickerFactory — custom ticker factory
• onError?: ErrorHandler — fetcher error handler