ChatGoogle doesn't work with streaming tools

[cpsievert]

This seems like a current limitation in Google Gemini itself -- see google-gemini/generative-ai-python#446

from chatlas import ChatGoogle, ToolDef

chat = ChatGoogle(system_prompt="Be very terse, not even punctuation.")
chat.register_tool(
    ToolDef(lambda: "2024-01-01", name="get_date", description="Gets the current date")
)

chat.chat("What's the current date in YMD format?", stream=True)

Traceback (most recent call last):
  File "/Users/cpsievert/github/chatlas/sandbox/assert_google.py", line 19, in <module>
    chat.chat(
  File "/Users/cpsievert/github/chatlas/chatlas/_chat.py", line 235, in chat
    self._chat_emit(user_turn(*args), stream=stream, kwargs=kwargs)
  File "/Users/cpsievert/github/chatlas/chatlas/_chat.py", line 351, in _chat_emit
    for part in response:
  File "/Users/cpsievert/github/chatlas/chatlas/_chat.py", line 387, in _chat_impl
    for chunk in self._submit_turns(user_turn_result, stream, kwargs=kwargs):
  File "/Users/cpsievert/github/chatlas/chatlas/_chat.py", line 424, in _submit_turns
    text = self.provider.stream_text(chunk)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/cpsievert/github/chatlas/chatlas/_google.py", line 201, in stream_text
    return chunk.text
           ^^^^^^^^^^
  File "/Users/cpsievert/github/chatlas/.venv/lib/python3.12/site-packages/google/generativeai/types/generation_types.py", line 536, in text
    part_type = protos.Part.pb(part).whichOneof("data")
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: whichOneof. Did you mean: 'WhichOneof'?