Fix PY3.13 support issues; drop PY3.8 support

[ktbyers]

PY3.8 is EOL.

Used vendored version of telnetlib inside of Netmiko; alternative is to completely drop telnet support (of find some alternatively maintained telnet library).

[ktbyers]

Another option is to just gracefully catch the import telnetlib failure such that it doesn't cause the Device import to fail.

Basically, create a deprecation warning and gracefully catch the import telnetlib failure. In this way, people using PY3.9 - PY3.12 could keep using telnetlib and PY3.13 would work for its main uses. telnet function would cease working in PY3.13 as it would be deprecated by PyEZ.

[a-detiste]

https://github.com/youknowone/python-deadlib provides telnetlib