Fix data file module inference
Hi ! datasets saved using `save_to_disk` should be loaded with `load_from_disk` ;) It is convienient to just pass in a path to a local dataset or one from the hub and use the same function to load it. Is it not possible to get this fix merged in to allow this?  We can modify `save_to_disk` to write the dataset in a structure supported by the Hub in this case, it's kind of a legacy function anyway
I saved a dataset with two splits to disk with `DatasetDict.save_to_disk`. The train is bigger and ended up in 10 shards, whereas the test split only resulted in 1 split.

Now when trying to load the dataset, an error is raised that not all splits have the same data format:

> ValueError: Couldn't infer the same data file format for all splits. Got {NamedSplit('train'): ('arrow', {}), NamedSplit('test'): ('json', {})}

This is not expected because both splits are saved as arrow files.

I did some debugging and found that this is the case because the list of data_files includes a `state.json` file. 

Now this means for train split I get 10 ".arrow" and 1 ".json" file. Since datasets picks based on the most common extension this is correctly inferred as "arrow". In the test split, there is 1 .arrow and 1 .json file. Given the function description:

> It picks the module based on the most common file extension.
    In case of a draw ".parquet" is the favorite, and then alphabetical order.

This is not quite true though, because in a tie the extensions are actually based on reverse-alphabetical order:
```
for (ext, _), _ in sorted(extensions_counter.items(), key=sort_key, *reverse=True*):
```

Which thus leads to the module wrongly inferred as "json", whereas it should be "arrow", matching the train split.

I first thought about adding "state.json" in the list of excluded files for the inference: https://github.com/huggingface/datasets/blob/main/src/datasets/load.py#L513. However, I think from digging into the code it looks like the right thing to do is to exclude it in the list of `data_files` to start with, because it is more of a metadata than a data file.