Fix crash/mutation/log bugs in the shared napalm utils and proxy

[ggiesen]

What does this PR do?

Fixes three bugs in the shared NAPALM machinery (salt/utils/napalm.py and
salt/proxy/napalm.py) that every NAPALM module and proxy sits on top of.

1. get_device_opts crashes on optional_args: null and mutates the caller's
   config. device_dict.get("optional_args", {}) returns None when the key is
   present but null (the default only applies to a missing key), so the
   "config_lock" not in ... membership test raised TypeError. And when
   optional_args was a dict, it was used by reference -- the config_lock /
   keepalive defaults injected below were written straight back into the user's
   live opts/pillar structure. Now copy.deepcopy(... or {}).

2. force_reconnect raises KeyError: 'proxy' on a straight minion.
   proxy_napalm_wrap did opts["proxy"].update(**kwargs) unconditionally, but a
   straight (non-proxy) NAPALM minion has no proxy key. That merge is only
   needed for the always-alive proxy path; a straight minion already picks the
   override up from clean_kwargs further down, so it's now guarded by
   is_proxy(opts).

3. proxy.shutdown logs a malformed port. A trailing comma made port a
   1-tuple, so a failed close() logged :(830,) / :(None,) (and the
   if port guard never suppressed the empty case). Comma removed.

What issues does this PR fix or reference?

Found by an audit of the NAPALM modules (same series as #69793 / #69794 /
#69795).

Note

The audit also found a salt.utils.napalm.call() reconnect issue -- in
not-always-alive mode, the inner open() during a ConnectionClosedException
retry is closed by its own finally before the command re-runs. It needs a more
careful fix plus a reconnect test harness, so it is intentionally left for a
follow-up rather than shipped unvalidated here.

This PR adds tests/pytests/unit/utils/test_napalm.py; #69793 also adds that
file (different test functions), so whichever merges second needs a trivial
combine.

Merge requirements satisfied?

• Docs
• Changelog
• Tests written/updated

test_get_device_opts_null_optional_args, test_get_device_opts_does_not_mutate_caller,
test_proxy_napalm_wrap_force_reconnect_straight_minion (new
utils/test_napalm.py) and test_shutdown_logs_scalar_port_on_close_failure
(added to proxy/test_napalm.py). All fail against the current code.

Commits signed with GPG?

No