Fix #791: HuggingFaceDataset doesn't shuffle the dataset

- datasets.Dataset.shuffle() returns a new Dataset object
- Need to assign the result: self._dataset = self._dataset.shuffle()
- Fixed in both __init__ and shuffle() methods
- Maintains backward compatibility

Fixes #791

Author: OpenClaw Assistant

textattack/datasets/huggingface_dataset.py

@@ -149,7 +149,7 @@ def __init__(
 
         self.shuffled = shuffle
         if shuffle:
-            self._dataset.shuffle()
+            self._dataset = self._dataset.shuffle()
 
     def _format_as_dict(self, example):
         input_dict = collections.OrderedDict(
@@ -190,5 +190,5 @@ def __getitem__(self, i):
             ]
 
     def shuffle(self):
-        self._dataset.shuffle()
+        self._dataset = self._dataset.shuffle()
         self.shuffled = True