Turn @config into a dataclass_transform (#31541)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

vllm/config/structured_outputs.py

@@ -4,7 +4,6 @@
 from typing import Any, Literal
 
 from pydantic import model_validator
-from pydantic.dataclasses import dataclass
 from typing_extensions import Self
 
 from vllm.config.utils import config
@@ -16,7 +15,6 @@ StructuredOutputsBackend = Literal[
 
 
 @config
-@dataclass
 class StructuredOutputsConfig:
     """Dataclass which contains structured outputs config for the engine."""