Class PushStoredChannelTransfer<T>

Reactive channel with last-value retention. Combines push/pull/subscribe/trigger.

Capabilities: isInput, isOutput, isPushable, isPullable, isSubscribable, isTriggerable

Mechanics:

1. push(data) — writes the value, notifies subscribers (does NOT clear _state)
2. pull() — reads the current value without clearing
3. subscribe(handler) — subscribes to notifications
4. trigger() — manually sends the current value to subscribers
5. destroy() — unsubscribes subscribers, clears state

Difference from PushChannelTransfer:

• Does not clear _state after push() — the value is available for pull()
• Has trigger() for manual emission without changing data

Use cases:

• Caching the last value with reactive updates
• Component state with manual synchronization capability
• Buffer with subscription to changes