style: sort FuturesContractError into the __init__ import block

ruff's isort rule failed CI: the new export was inserted before
ValidationError rather than in alphabetical position after DataNotFoundError.
No behaviour change.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015ao5paex73xXvuM424Libo

Author: karlwaldman

oilpriceapi/__init__.py

@@ -18,14 +18,14 @@
     BadRequestError,
     ConfigurationError,
     DataNotFoundError,
+    FuturesContractError,
     NetworkError,
     OilPriceAPIError,
     PaymentRequiredError,
     PermissionDeniedError,
     RateLimitError,
     ServerError,
     TimeoutError,
-    FuturesContractError,
     ValidationError,
 )
 from oilpriceapi.models import (