Improce VLM API model calls

Hi @PeterStaar-IBM, @dolfim-ibm and @cau-git,
This update is really great thanks, I tested it and works really well. I have some Optimization suggestions for the remote api solution:
- [ ] Can you please add a retry option (int), to say how many times the requests should retry when it failed ? As OpenAI SDK does ? https://github.com/openai/openai-python?tab=readme-ov-file#retries
- [ ] It would be nice of having the possibility to configure the http client (something like httpx ), so that it can help to configure extra things like proxies...
- [x] What about giving the possibility to run the request of all (or a group of) pages in parallel, so that we must not wait for one page before asking the markdown of the next page. and then with something like asyncio.gather sort them all when it is done. It can really be a time saver.

Thanks for the great work you are doing it's really amazing 💪

_Originally posted by @KapyGenius in https://github.com/docling-project/docling/issues/1570#issuecomment-2950168806_