fix livekit-api types

[theomonnom]

Fix:

Traceback (most recent call last):
  File "/Users/theomonnom/livekit/agents/examples/voice_agents/structured_output.py", line 10, in <module>
    from livekit.agents import (
  File "/Users/theomonnom/livekit/agents/livekit-agents/livekit/agents/__init__.py", line 15, in <module>
    from . import cli, ipc, llm, metrics, stt, tokenize, tts, utils, vad  # noqa: F401
  File "/Users/theomonnom/livekit/agents/livekit-agents/livekit/agents/cli/__init__.py", line 1, in <module>
    from .cli import run_app
  File "/Users/theomonnom/livekit/agents/livekit-agents/livekit/agents/cli/cli.py", line 15, in <module>
    from ..worker import JobExecutorType, Worker, WorkerOptions
  File "/Users/theomonnom/livekit/agents/livekit-agents/livekit/agents/worker.py", line 39, in <module>
    from livekit import api, rtc
  File "/Users/theomonnom/livekit/python-sdks/livekit-api/livekit/api/__init__.py", line 38, in <module>
    from .livekit_api import LiveKitAPI
  File "/Users/theomonnom/livekit/python-sdks/livekit-api/livekit/api/livekit_api.py", line 6, in <module>
    from .sip_service import SipService
  File "/Users/theomonnom/livekit/python-sdks/livekit-api/livekit/api/sip_service.py", line 40, in <module>
    class SipService(Service):
  File "/Users/theomonnom/livekit/python-sdks/livekit-api/livekit/api/sip_service.py", line 188, in SipService
    transport: Optional[SIPTransport] = None,
  File "/opt/homebrew/Cellar/python@3.9/3.9.19/Frameworks/Python.framework/Versions/3.9/lib/python3.9/typing.py", line 277, in inner
    return func(*args, **kwds)
  File "/opt/homebrew/Cellar/python@3.9/3.9.19/Frameworks/Python.framework/Versions/3.9/lib/python3.9/typing.py", line 354, in __getitem__
    return self._getitem(self, parameters)
  File "/opt/homebrew/Cellar/python@3.9/3.9.19/Frameworks/Python.framework/Versions/3.9/lib/python3.9/typing.py", line 478, in Optional
    arg = _type_check(parameters, f"{self} requires a single type.")
  File "/opt/homebrew/Cellar/python@3.9/3.9.19/Frameworks/Python.framework/Versions/3.9/lib/python3.9/typing.py", line 166, in _type_check
    raise TypeError(f"{msg} Got {arg!r:.100}.")
TypeError: typing.Optional requires a single type. Got <google.protobuf.internal.enum_type_wrapper.EnumTypeWrapper object at 0x109e27070>.

[davidzhao]

thank you!