Autodiscovery not supported for SCPI-Telnet and SCPI-Raw devices

[snhobbs]

TCPIPSocketSession has a stub for list_resources:

@staticmethod
def list_resources() -> List[str]:
    # TODO: is there a way to get this?
    return []

So any raw sockets and telnet devices are not automatically discoverable.
If a device does advertise services then the same get_services method as used in TCPIPInstrVicp, TCPIPInstrHiSLIP can use used to look for _scpi-raw._tcp.local and _scpi-telnet._tcp.local. Since there are standard ports for scpi-telnet (5024) and scpi-raw (5025) there could be a fallback option for port scan for devices without mDNS.