refactor: streamline result processing in structured output parser

- Converted the result processing logic into a generator function for improved memory efficiency and clarity.
- Maintained the existing functionality while enhancing the structure of the code for better readability.

api/core/llm_generator/output_parser/structured_output.py

@@ -142,6 +142,8 @@ def invoke_llm_with_structured_output(
             prompt_messages=llm_result.prompt_messages,
         )
     else:
+
+        def generator():
             result_text = ""
             for event in llm_result:
                 if isinstance(event, LLMResultChunk):
@@ -150,6 +152,8 @@ def invoke_llm_with_structured_output(
 
             yield LLMStructuredOutput(structured_output=_parse_structured_output(result_text))
 
+        return generator()
+
 
 def _handle_native_json_schema(
     provider: str,