Fix napalm.junos_rpc get-config filter leaking the __kwarg__ marker (#65867)

[ggiesen]

What does this PR do?

Fixes junos.rpc (used by napalm.junos_rpc) so a get-config call with a filter works again.

junos.rpc builds its RPC options (op) from __pub_arg, which carries the reserved __kwarg__ marker that the Salt CLI appends to keyword arguments. That marker leaked into the RPC options; on the get-config path junos-eznc's ElementMaker then tried to render the True value as an XML attribute and raised KeyError: <class 'bool'>, so the filter option stopped working after upgrading from 3004 to 3006.

The fix strips dunder keys from op with salt.utils.args.clean_kwargs (already used by junos.diff) right after op is assembled, so reserved markers are dropped on both the get-config and the generic RPC branch.

Fixes

Fixes #65867

Tests

Adds two regression tests in tests/pytests/unit/modules/test_junos.py:

• test_rpc_get_config_filter_ignores_kwarg_marker - the reported case: __pub_arg carries {'filter': ..., '__kwarg__': True} and the rendered RPC must be the clean <get-configuration format="xml">...</get-configuration>.
• test_rpc_non_get_config_ignores_kwarg_marker - the generic path, where op is forwarded as RPC arguments rather than options.

Both fail without the fix (the get-config case raises KeyError: <class 'bool'> in junos-eznc's ElementMaker) and pass with it, verified against real junos-eznc (2.8.2) rendering with only Device.execute mocked.

Notes

The same __pub_arg handling block is repeated in several other junos functions (e.g. cli, commit, install_config). This PR is scoped to the reported get-config regression; applying the same marker stripping to the other functions can follow separately.

[ggiesen]

Validated against a live Junos device (junos-eznc 2.8.2, NETCONF over SSH), running the reporter's exact path:

• Without this change, napalm.junos_rpc get_config filter=... raises KeyError: <class 'bool'> inside junos-eznc's ElementMaker at E("get-configuration", options), because the RPC options carry {'__kwarg__': True}.
• With this change, the options are {'format': 'xml'} and the same call returns the requested configuration normally.

That's the same mechanism the added unit tests cover (only Device.execute is mocked there, so the real RPC element is still rendered).

[twangboy]

Looks like you have some test failures

[ggiesen]

Thanks @twangboy -- those were the functional zeromq jobs hitting the 6-hour runner timeout on a superseded run, not real failures. The re-run on the same commit is green and the merge state is clean now.

[twangboy]

It's the most beautiful thing I've ever seen