Mechanical: ruff format, and ruff check --fix with the rule set every NAPALM
driver uses (E, F, I, UP, B at line length 100, Python 3.10). What ruff
cannot fix comes in the next commit.
The driver accepted any SSH host key. It now verifies through
napalm-device-types' HostKeyCheck (>= 4.19.0): with a known key in
optional_args["ssh_host_keys"] any other key is refused before login, and
every key seen is reported to optional_args["ssh_host_key_observer"].
Without either argument it connects as before (first use).