feat: add ContinuousUpdates extension and repeater progress events
ContinuousUpdates Extension (RFC 6143):
- Add pseudo-encoding -313 for client capability advertisement
- Send EndOfContinuousUpdates (msg 150) when client advertises support
- Handle EnableContinuousUpdates message to enable/disable push updates
- When enabled, server pushes updates without FramebufferUpdateRequest
- When disabled, use traditional request-response model
Repeater Progress Events:
- Add RfbMessageSent event (emitted when RFB ID sent to repeater)
- Add HandshakeComplete event (emitted when VNC handshake completes)
- Add request_id tracking for correlating connection events
- Add connect_repeater_with_request_id() and connect_repeater_with_progress()
Both features maintain backward compatibility with existing APIs.
