Add provider for Anthropic's Vertexai Client

[ehaca]

Hello folks,
I had some time and started drafting a possible implementation for this issue: #960.
There's still lots of work to do, but I was feeling kind of insecure about my approach and wanted to get some (both general and concrete) feedback if possible before investing more time on it :)

My main questions are:

1. Is the idea about creating yet another extra something of your liking?
2. The Pycharm typing issue about

 def __init__(
        self,
        model_name: AnthropicModelName,
        *,
        # breaking this in multiple lines breaks pycharm type recognition. However, I was unable to stop ruff from
        # doing it - # fmt: skip etc didn't work  :(
        provider: Literal['anthropic', 'anthropic-vertex']
        | Provider[AsyncAnthropicVertex]
        | Provider[AsyncAnthropic] =  # fmt: skip
        'anthropic',
    ):

2. Now I am getting some static typing errors for test_init in tests/models/test_anthropic.py, how should I handle this?

Thank you very much for your feedback and help and have a nice day :)

[Kludex]

I think you need to do # fmt: off and # fmt: on after.

[acostajohn]

Maybe you should also add an entry to the KnownModelName literal at models/__init__.py

[Kludex]

This is tricky. If you want google-vertex:<anthropic-model>, the agent should be able to infer this provider instead of the other... Maybe the provider should offer different clients depending on the model?

Right now, the GoogleVertexProvider is a generic on the client, which currently is httpx.AsyncClient. What the provider can offer a client via method?

class GoogleVertexProvider(Provider):
    def get_client(self, tp: type[T]) -> T:
        if isinstance(tp, httpx.AsyncClient):
            return self.httpx_client
        elif isinstance(tp, AsyncAnthropicVertex):
            return self.anthropic_client
        else:
            raise ValueError('not supported')