Support numpy/torch/tf/jax formatting for IterableDataset
hii @lhoestq, can you assign this issue to me? Though i am new to open source still I would love to put my best foot forward. I can see there isn't anyone right now assigned to this issue. Hi @zutarich ! This issue was fixed by #5852 - sorry I forgot to close it

Feel free to look for other issues and ping me or @mariosasko if you have questions :)
Also let us know if we can help find an issue that can correspond to what you're looking for
Right now `IterableDataset` doesn't do any formatting.

In particular this code should return a numpy array:
```python
from datasets import load_dataset

ds = load_dataset("imagenet-1k", split="train", streaming=True).with_format("np")
print(next(iter(ds))["image"])
```

Right now it returns a PIL.Image.

Setting `streaming=False` does return a numpy array after #5072 