fix ruff formatting in _volumes.py

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: tamirse

verda/volumes/_volumes.py

@@ -60,7 +60,6 @@ class Volume:
     currency: str | None = None
     long_term: dict | None = None
 
-
     @classmethod
     def create_from_dict(cls, volume_dict: dict) -> 'Volume':
         """Create a Volume object from a dictionary.