Fix dataclasses.asdict on the msgspec ServerArgs (#38958)

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

examples/runtime/engine/offline_batch_inference_async.py

@@ -9,9 +9,10 @@ which is useful to implement an online-like generation with batched inference.
 
 import argparse
 import asyncio
-import dataclasses
 import time
 
+import msgspec
+
 import sglang as sgl
 from sglang.srt.server_args import ServerArgs
 
@@ -26,7 +27,7 @@ class InferenceEngine:
 
 
 async def run_server(server_args):
-    inference = InferenceEngine(**dataclasses.asdict(server_args))
+    inference = InferenceEngine(**msgspec.structs.asdict(server_args))
 
     # Sample prompts.
     prompts = [