Fix argparse help output broken by bb1e7a8617

[howeaj]

Fixes the crashes that prevent help from ever being generated for emu commands. For example:

> pebble emu-button
Traceback (most recent call last):
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 1965, in _parse_known_args2
    namespace, args = self._parse_known_args(args, namespace, intermixed)
                      ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 2262, in _parse_known_args
    raise ArgumentError(None, _('the following arguments are required: %s') %
               ', '.join(required_actions))
argparse.ArgumentError: the following arguments are required: action

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/ajh/.local/bin/pebble", line 10, in <module>
    sys.exit(run_tool())
             ~~~~~~~~^^
  File "/home/ajh/.local/share/uv/tools/pebble-tool/lib/python3.13/site-packages/pebble_tool/__init__.py", line 54, in run_tool
    args = parser.parse_args(args)
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 1926, in parse_args
    args, argv = self.parse_known_args(args, namespace)
                 ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 1936, in parse_known_args
    return self._parse_known_args2(args, namespace, intermixed=False)
           ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 1965, in _parse_known_args2
    namespace, args = self._parse_known_args(args, namespace, intermixed)
                      ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 2220, in _parse_known_args
    stop_index = consume_positionals(start_index)
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 2172, in consume_positionals
    take_action(action, args)
    ~~~~~~~~~~~^^^^^^^^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 2041, in take_action
    action(self, namespace, argument_values, option_string)
    ~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 1286, in __call__
    subnamespace, arg_strings = subparser.parse_known_args(arg_strings, None)
                                ~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 1936, in parse_known_args
    return self._parse_known_args2(args, namespace, intermixed=False)
           ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 1967, in _parse_known_args2
    self.error(str(err))
    ~~~~~~~~~~^^^^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 2684, in error
    self.print_usage(_sys.stderr)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 2651, in print_usage
    self._print_message(self.format_usage(), file)
                        ~~~~~~~~~~~~~~~~~^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 2616, in format_usage
    return formatter.format_help()
           ~~~~~~~~~~~~~~~~~~~~~^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 287, in format_help
    help = self._root_section.format_help()
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 216, in format_help
    item_help = join([func(*args) for func, args in self.items])
                      ~~~~^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 325, in _format_usage
    action_usage = format(optionals + positionals, groups)
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 393, in _format_actions_usage
    return ' '.join(self._get_actions_usage_parts(actions, groups))
                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 396, in _get_actions_usage_parts
    parts, _ = self._get_actions_usage_parts_with_split(actions, groups)
               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/home/ajh/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/argparse.py", line 412, in _get_actions_usage_parts_with_split
    raise ValueError(f'empty group {group}')
ValueError: empty group <argparse._MutuallyExclusiveGroup object at 0x70247493b850>