[BugFix] fix default parser (#3932)

* add reasoning parser plugin

* fix finish reason

* fix default parser

---------

Co-authored-by: Yuanle Liu <yuanlehome@163.com>
Co-authored-by: Jiang-Jia-Jun <163579578+Jiang-Jia-Jun@users.noreply.github.com>

Author: 3 people

fastdeploy/input/preprocess.py

@@ -76,7 +76,9 @@ def create_processor(self):
                 load_reasoning_parser_plugins,
             )
 
-            reasoning_parser_obj = load_reasoning_parser_plugins()
+            custom_reasoning_parser = load_reasoning_parser_plugins()
+            if self.reasoning_parser == "custom_reasoning_parser":
+                reasoning_parser_obj = custom_reasoning_parser
         except:
             if self.reasoning_parser:
                 reasoning_parser_obj = ReasoningParserManager.get_reasoning_parser(self.reasoning_parser)