Accessing Arrow dataset cache_files
Thanks @bhavitvyamalik for referencing the workaround. Setting `keep_in_memory=False` is working.
## Describe the bug
In datasets 1.5.0 the following code snippet would have printed the cache_files:

```
train_data = load_dataset('conll2003', split='train', cache_dir='data')
print(train_data.cache_files[0]['filename'])

```

However, in the newest release (1.6.1), it prints an empty list.

I also tried loading the dataset with `keep_in_memory=True` argument but still `cache_files` is empty.

Was wondering if this is a bug or I need to pass additional arguments so I can access the cache_files.
