Class StoredChannelTransfer<T>

Output channel with last-value retention and external management.

Capabilities: isOutput, isPullable, isTriggerable, isSubscribable

Mechanics:

1. The constructor accepts config with setup/destroy callbacks (like ChannelTransfer)
2. setup() calls emit(data), which writes the value to _state and calls trigger()
3. trigger() — notifies subscribers with the current value (without clearing _state)
4. pull() — reads the current value without clearing
5. subscribe(handler) — subscribes to notifications
6. destroy() — calls config.destroy(), unsubscribes subscribers

Error handling:

• onError — for errors in emit() (when sending data to subscribers)
• onDestroyError — for errors in destroy()
• With the corresponding handler provided, the exception is suppressed.
• Without a handler, the exception is rethrown.
• setup() errors are always rethrown (no onSetupError).

Configuration (StoredChannelTransferConfig):

• setup: (emit: DataHandler) => void — channel initialization
• destroy: () => void — channel cleanup
• initialValue?: T — initial value in _state
• onError?: ErrorHandler — emit() error handler
• onDestroyError?: ErrorHandler — destroy() error handler

Difference from ChannelTransfer:

• Retains the last value (pull() is available)
• Has trigger() for re-emitting the current value
• emit() calls trigger() instead of sendState() + clear()

Use cases:

• Integration with external sources with caching
• Channel with the ability to re-read the last value
• Storing state from an external source