Add Support for `telnetlib3` as `telnetlib` is Deprecated from Python 3.11+

[engineerjoe440]

Python's built-in telnetlib is being deprecated in Python 3.11 (see PEP 594), and should be migrated towards telnetlib3.

telnetlib3 is an asyncio-capable library, and some modifications will need to be made, accordingly. Still, they've got a nice example of a client in their README:

import asyncio, telnetlib3

@asyncio.coroutine
def shell(reader, writer):
    while True:
        # read stream until '?' mark is found
        outp = yield from reader.read(1024)
        if not outp:
            # End of File
            break
        elif '?' in outp:
            # reply all questions with 'y'.
            writer.write('y')

        # display all server output
        print(outp, flush=True)

    # EOF
    print()

loop = asyncio.get_event_loop()
coro = telnetlib3.open_connection('localhost', 6023, shell=shell)
reader, writer = loop.run_until_complete(coro)
loop.run_until_complete(writer.protocol.waiter_closed)

Furthermore, it appears that the client.open_connection method will return a tuple of the reader/writer objects that can be used with other logic. Perhaps they could be sent as a tuple to the SELClient object?