Improve typing of Dataset.search, matching definition
Previously, the output of `score, indices = Dataset.search(...)` would be numpy arrays.

The definition in `SearchResult` is a `List[int]` so this PR now matched the expected type.

The previous behavior is a bit annoying as `Dataset.__getitem__` doesn't support `numpy.int64` which forced me to convert `indices` to int eg:

```python
score, indices = ds.search(...)
item = ds[int(indices[0])]
```
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_6816). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update. Hi! This is a breaking change. A better solution is to check for "indexable" types in `__getitem__` to support keys such as `np.int64`:
```python
import operator

def _query_table_with_indices_mapping(...):  # or _query_table
    ...
    try:
        operator.index(key)
    except TypeError:
        pass
 
    _raise_bad_key_type(key)
``` Sounds good! We should still update type annotations for SearchResult in my opinion.