Class AsyncConvertTransfer<TInput, TOutput>

Async converter transfer: transforms input data via an AsyncOperator and sends the result to subscribers.

Capabilities: isInput, isOutput, isDuplex, isAsyncPushable, isSubscribable

Mechanics:

1. The constructor accepts config.operator: AsyncOperatorInterface<TInput, TOutput | undefined>
2. asyncPush(data) — applies await operator.apply(data), notifies subscribers, clears _state
3. subscribe(handler) — subscribes to transformed data (sync)
4. If the operator returns undefined — subscribers are not notified

Sequence Guard (active when maxConcurrency > 1):

• Multiple operator.apply() calls run in parallel (up to maxConcurrency).
• Results are emitted to subscribers strictly in data-arrival order.
• A faster operation that completes before an older one waits in an internal pending queue until its predecessor is emitted.
• This prevents a stale result from overwriting a fresh one in _state.value.
• When maxConcurrency <= 1, the guard is inactive (no overhead).

Error handling:

• If operator.apply() throws an exception, onError is called.
• With onError provided, the exception is suppressed. Without onError — rethrown.
• When the guard is active, a failed operation submits undefined to the queue so that subsequent results are not blocked.

Configuration (AsyncConvertTransferConfig):

• operator: AsyncOperatorInterface<TInput, TOutput | undefined>
• onError?: ErrorHandler
• maxConcurrency?, bufferSize?, onBufferOverflow? (BackpressureConfig)