Include the signature

Author: mwildehahn

pydantic_ai_slim/pydantic_ai/_parts_manager.py

@@ -171,7 +171,7 @@ def handle_thinking_delta(
             if content is not None:
                 # There is no existing thinking part that should be updated, so create a new one
                 new_part_index = len(self._parts)
-                part = ThinkingPart(content=content)
+                part = ThinkingPart(content=content, signature=signature)
                 if vendor_part_id is not None:
                     self._vendor_id_to_part_index[vendor_part_id] = new_part_index
                 self._parts.append(part)