Arrow Dataset adoptability

[parmidaatg]

Describe the bug
Arrow dataset and more precisely HFdatasets won't be indexable with type "numpy.int64" we need to fix this again.

To Reproduce
given train_set is a HFDataset,

active_dataset = ActiveLearningDataset(train_set)
active_dataset.label_randomly(10)
print(active_dataset[0])

Output:

activelearning dataset <baal.active.dataset.pytorch_dataset.ActiveLearningDataset object at 0x7f679f85ca30>```

**Vesion (please complete the following information):**
 - OS: _
 - Python: 3.8
 - BaaL version: 1.5.0