Support parallel function calls with tool_choice

[CISC]

Enable the return of parallel function calls when tool_choice is set to a specific function, previously you would only get the following response for get_current_weather and the prompt What's the weather like in Oslo and Stockholm?:

[
    {
        "id": "call__0_get_current_weather_cmpl-...",
        "type": "function",
        "function": {
            "name": "get_current_weather",
            "arguments": "{\"location\": \"Oslo, NO\", \"unit\": \"celsius\"}"
        }
    }
]

Now you will get all the get_current_weather calls:

[
    {
        "id": "call__0_get_current_weather_cmpl-...",
        "type": "function",
        "function": {
            "name": "get_current_weather",
            "arguments": "{\"location\": \"Oslo, NO\", \"unit\": \"celsius\"}"
        }
    },
    {
        "id": "call__1_get_current_weather_cmpl-...",
        "type": "function",
        "function": {
            "name": "get_current_weather",
            "arguments": "{\"location\": \"Stockholm, SE\", \"unit\": \"celsius\"}"
        }
    },
]

Additionally the function call names will now be verified (and filtered if not matching), whereas before there was the possibility of picking up a different function call with similar parameters.

[lsorber]

I opened #1884 with a number of improvements to chatml-function-calling, including streaming tool use and fixing parallel function calling.