[Bugfix] Streamed tool calls now more strictly follow OpenAI's format; ensures Vercel AI SDK compatibility

[K-Mistele]

This PR fixes tool streaming so that streamed tool call chunks pass the Vercel AI SDK's validations on chunk structure. While the existing chunk structure for tool streaming is OpenAI-compatible for most purposes (including use with the OpenAI SDK), the structure was apparently not 100% correct.

This PR fixes that. vLLM's tool calling API (streaming and non-streaming) is now fully OpenAI-compatible.
This means that you can use vLLM with the vercel AI SDK and the createOpenAI method in that SDK, like so:

import {createOpenAI } from '@ai-sdk/openai'
import {streamText} from 'ai'

const hermes = createOpenAI({
    compatibility: 'strict', // required if you want usage :)
    apiKey: process.env.OPENAI_API_KEY,
    baseURL: process.env.OPENAI_API_BASE,
}).chat(process.env.OPENAI_MODEL!)

const result = await streamText({
    model: hermes,
    tools: {...},
    ...
})

Note that based on testing, setting compatibility: 'strict' is required for some features like usage stats to work out-of-the-box.

I found a related issue vercel/ai#2231 that this should solve.

I promise this is the last fix before I get to Llama 3.1 :P

cc @mgoin @DarkLight1337

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[github-actions]

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[mgoin]

There are print statements and a TODO comment - is this ready?

[K-Mistele]

There are print statements and a TODO comment - is this ready?

sorry about that, just cleaned it up. It is now.

[K-Mistele]

are all AMD tests expected to be failing?

[DarkLight1337]

are all AMD tests expected to be failing?

AMD tests are unstable atm, you can ignore them if the failure is unrelated to the PR.

[mgoin]

Excellent, LGTM!