Class BufferTransfer<T>

Passive buffer with push/pull mechanics (no notifications).

Capabilities: isInput, isOutput, isPushable, isPullable

Mechanics:

1. push(data) — writes the value (overwrites the previous one)
2. pull() — extracts the value WITH CLEANUP (uses _state.pop())

Differences from PushStoredChannelTransfer:

• No subscription (subscribe) — only active pull()
• No trigger — data is not sent automatically
• pull() clears the buffer (pop) rather than just reading

Use cases:

• One-time data transfer between processes
• Buffer for producer-consumer pattern without reactivity
• Synchronous data exchange on demand