Add connection state check to transceiveValue.

Previously the transmission of value requests continued even when the
underlying connection has been interrupted or disconnected. This patch
adds checks and suspends transceiving while the connection is trying
to reestablish.
Refactor DLxRecorder to enhance testability.

This patch introduces a `_request` helper method that normally
forwards all parameters to the request module and returns the result.
Add DLxRecorder tests.
Enable random port choice for TcpConnection tests.
Fix bug regarding wrong `optimizer` prop in Customizer.