[Refactor] Lazy-loaded reasoning_parser (#28092)

Signed-off-by: chaunceyjiang <chaunceyjiang@gmail.com>

vllm/reasoning/step3_reasoning_parser.py

@@ -8,12 +8,11 @@ from transformers import PreTrainedTokenizerBase
 
 from vllm.entrypoints.openai.protocol import ChatCompletionRequest, DeltaMessage
 from vllm.logger import init_logger
-from vllm.reasoning import ReasoningParser, ReasoningParserManager
+from vllm.reasoning import ReasoningParser
 
 logger = init_logger(__name__)
 
 
-@ReasoningParserManager.register_module("step3")
 class Step3ReasoningParser(ReasoningParser):
     """
     Reasoning parser for Step3 model.