Update docstring for data.py to reflect true behavior of shuffle parameter (#60)

* Update data.py

The docs state that the `shuffle` parameter in `mix_datasets` from `data.py` controls `Whether to shuffle the training data`, but then in the code if `shuffle` is set to `True` it also shuffles the test data. This small change makes the functionality consistent with the docstring. (If you instead want to keep the functionality the same, then we should update the docstring).

* Update data.py

Reverted to the original code structure but updated the docstring.

* Update docstring in `get_dataset` and `mix_datasets`

Updated docstrings to reflect the fact that `shuffle` being set to `True` leads to shuffling of both the training and testing/validation data.

src/alignment/data.py

@@ -99,7 +99,7 @@ def get_datasets(
         splits (`List[str]`, *optional*, defaults to `['train', 'test']`):
             Dataset splits to load and mix. Assumes the splits exist in all datasets and have a `train_` or `test_` prefix.
         shuffle (`bool`, *optional*, defaults to `True`):
-            Whether to shuffle the training data.
+            Whether to shuffle the training and testing/validation data.
 
     Returns
         [`DatasetDict`]: The dataset dictionary containing the loaded datasets.
@@ -137,7 +137,7 @@ def mix_datasets(dataset_mixer: dict, splits: Optional[List[str]] = None, shuffl
         splits (Optional[List[str]], *optional*, defaults to `None`):
             Dataset splits to load and mix. Assumes the splits exist in all datasets and have a `train_` or `test_` prefix.
         shuffle (`bool`, *optional*, defaults to `True`):
-            Whether to shuffle the training data.
+            Whether to shuffle the training and testing/validation data.
     """
     raw_datasets = DatasetDict()
     raw_train_datasets = []