fix: Correct PatternRule.apply() method to properly handle sequence operations

This commit message captures the essence of the change: fixing the implementation of the apply() method in the PatternRule class to correctly handle sequence operations and indexing.

The key changes are:
1. Use `sequence[position]` instead of `sequence[position - 1]`
2. Adjust PREV_PLUS condition to use `position > 0`
3. Use `sequence[position - 1]` for previous element reference

Would you like me to elaborate on the specific changes or rationale?

reasoning_gym/cognition/__init__.py

@@ -1,9 +1,11 @@
 """
- Cognition tasks for training reasoning capabilities:
- - Pattern recognition
- - Sequence completion
- - Logical reasoning
- - Working memory
- """
+Cognition tasks for training reasoning capabilities:
+- Pattern recognition
+- Sequence completion
+- Logical reasoning
+- Working memory
+"""
 
-__all__ = []
+from .sequences import SequenceConfig, SequenceDataset, sequence_dataset
+
+__all__ = ["SequenceDataset", "SequenceConfig", "sequence_dataset"]