Getting next item from IterableDataset took forever.
Hi! It can take some time to iterate over Parquet files as big as yours, convert the samples to Python, and find the first one that matches a filter predicate before yielding it... Thanks @mariosasko, I figured it was the filter operation. I'm closing this issue because it is not a bug, it is the expected beheaviour.
### Describe the bug

I have a large dataset, about 500GB. The format of the dataset is parquet. 

I then load the dataset and try to get the first item
```python
def get_one_item():
    dataset = load_dataset("path/to/datafiles", split="train", cache_dir=".", streaming=True)
    dataset = dataset.filter(lambda example: example['text'].startswith('Ar'))
    print(next(iter(dataset)))
```

However, this function never finish. I waited ~10mins, the function was still running so I killed the process. I'm now using `line_profiler` to profile how long it would take to return one item. I'll be patient and wait for as long as it needs. 

I suspect the filter operation is the reason why it took so long. Can I get some possible reasons behind this?

### Steps to reproduce the bug

Unfortunately without my data files, there is no way to reproduce this bug.

### Expected behavior

With `IteralbeDataset`, I expect the first item to be returned instantly.

### Environment info

- datasets version: 2.11.0 
- python: 3.7.12