refactor: Clean up assertion formatting and message handling in LocalBackend

- Simplified the message assignment logic in LocalBackend for better readability.
- Improved the formatting of assertions to enhance clarity.

These changes contribute to cleaner and more maintainable code in the LocalBackend class.

Author: bradhilton

src/art/local/backend.py

@@ -416,9 +416,7 @@ def _trajectory_log(self, trajectory: Trajectory) -> str:
             if isinstance(message_or_choice, dict):
                 message = message_or_choice
             else:
-                message = cast(
-                    Message, message_or_choice.message.model_dump()
-                )  # ty:ignore[possibly-missing-attribute]
+                message = cast(Message, message_or_choice.message.model_dump())  # ty:ignore[possibly-missing-attribute]
             formatted_messages.append(format_message(message))
         return header + "\n".join(formatted_messages)
 
@@ -704,9 +702,9 @@ async def _train_model(
             num_gradient_steps = int(
                 result.pop("num_gradient_steps", estimated_gradient_steps)
             )
-            assert (
-                num_gradient_steps == estimated_gradient_steps
-            ), f"num_gradient_steps {num_gradient_steps} != estimated_gradient_steps {estimated_gradient_steps}"
+            assert num_gradient_steps == estimated_gradient_steps, (
+                f"num_gradient_steps {num_gradient_steps} != estimated_gradient_steps {estimated_gradient_steps}"
+            )
             results.append(result)
             yield {**result, "num_gradient_steps": num_gradient_steps}
             pbar.update(1)