Feat: Enable will_continue-like function tools

[Lin-Nikaido]

feat: enable will_continue-like tool response.

It expected the tool returns generator, and the runner.async_run method yields the generator result as each Event.

I expect this usecase is the function-tool will take few minutes total, and you want to notice user its progress.
e.g. Like this function.

def search_tool(query: str):
    """ Example
    The query gives like " Answer to the Ultimate Question of Life, the Universe, and Everything".
    """
    yield {
        {
            "status": "inProgress",
            "message": f"searching Google with `{query}`"
        },
    }
    # Searching will take few second...
    link_list = ["https://hitsite1.com", "https://hitsite2.com", "https://hitsite3.com"]
    yield {
        {
            "status": "inProgress",
            "message": f"accessing each sites.\n{json.dumps(link_list, indent=2, ensure_ascii=False)}"
        },
    }
    # access these, retrieve information and analyze.
    yield {
        {
            "status": "inProgress",
            "message": f"summarizing the information."
        },
    }
    # summarizing each analyzed information.
    yield {
        {
            "status": "ok",
            "message": "42"
        },
    }

how to use

the ADK user no needed to any change. just the user can use genetor tool!