Turn @config into a dataclass_transform (#31541)

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

vllm/config/attention.py

@@ -4,14 +4,12 @@
 from typing import Any, Literal
 
 from pydantic import field_validator
-from pydantic.dataclasses import dataclass
 
 from vllm.config.utils import config
 from vllm.v1.attention.backends.registry import AttentionBackendEnum
 
 
 @config
-@dataclass
 class AttentionConfig:
     """Configuration for attention mechanisms in vLLM."""