refactor: add type hint to generator function in structured output parser

- Enhanced the generator function with a return type hint for improved type safety and clarity.
- Maintained existing functionality while improving code readability and maintainability.

api/core/llm_generator/output_parser/structured_output.py

@@ -143,7 +143,7 @@ def invoke_llm_with_structured_output(
         )
     else:
 
-        def generator():
+        def generator() -> Generator[LLMStructuredOutput, None, None]:
             result_text = ""
             for event in llm_result:
                 if isinstance(event, LLMResultChunk):