[Feature Request] Add beam search text streaming visualization feature

[MosheOfer1]

Feature request

Feature request

Remove the limitation that prevents using streamers with beam search. Currently, there's an error in the generation code:

if streamer is not None and (generation_config.num_beams > 1):
   raise ValueError(
       "`streamer` cannot be used with beam search (yet!). Make sure that `num_beams` is set to 1."
   )

### Motivation

### Motivation
When working with beam search generation, it's often difficult to understand why the model makes certain choices or how the beams evolve during generation. While debugging some beam search behavior, I discovered the `MultiBeamTextStreamer` class, but it took me some time to find it as it wasn't prominently featured in the documentation.

From an educational perspective, this tool is extremely valuable. Being able to visualize multiple beams in real-time provides an excellent way to teach and understand how beam search actually works. Students and educators could see the algorithm's decision-making process step by step, making abstract concepts concrete and interactive.

Making this feature more visible and providing better examples would help users who need to:
- Learn/teach beam search concepts interactively
- Debug beam search issues
- Understand model decision-making
- Create interactive demos

This improvement would make beam search less of a "black box" and provide a powerful educational tool for the NLP community.

### Your contribution

### Your contribution
I have implemented the MultiBeamTextStreamer class with tests and documentation. I plan to submit a PR for review after final cleanup. Would love early feedback on this approach.

Example of usage:
https://huggingface.co/spaces/mosheofer1/multi_beam_text_streamer

[LysandreJik]

cc @gante @zucchini-nlp