[Bugfix] Register serializers for V0 MQ Engine (#15009)

Signed-off-by: simon-mo <simon.mo@hey.com>

vllm/entrypoints/openai/api_server.py

@@ -82,6 +82,8 @@ from vllm.entrypoints.openai.serving_transcription import (
 from vllm.entrypoints.openai.tool_parsers import ToolParserManager
 from vllm.entrypoints.utils import load_aware_call, with_cancellation
 from vllm.logger import init_logger
+from vllm.transformers_utils.config import (
+    maybe_register_config_serialize_by_value)
 from vllm.usage.usage_lib import UsageContext
 from vllm.utils import (FlexibleArgumentParser, get_open_zmq_ipc_path,
                         is_valid_ipv6_address, set_ulimit)
@@ -221,6 +223,9 @@ async def build_async_engine_client_from_engine_args(
         # so we need to spawn a new process
         context = multiprocessing.get_context("spawn")
 
+        # Ensure we can serialize transformer config before spawning
+        maybe_register_config_serialize_by_value()
+
         # The Process can raise an exception during startup, which may
         # not actually result in an exitcode being reported. As a result
         # we use a shared variable to communicate the information.