fix(process_response): use issubclass instead of isinstance for ParallelBase check

The response_model parameter is a class (type), not an instance. Using
isinstance() on a class checks if that class is an instance of a type,
which always returns False for user-defined classes.

Changed from:
  if isinstance(response_model, ParallelBase):

To:
  if inspect.isclass(response_model) and issubclass(response_model, ParallelBase):

This fixes the "'generator' object has no attribute '_raw_response'" error
when using ParallelTools with models like Qwen3-VL.

Fixes #2049

Author: Mr-Neutr0n

instructor/processing/response.py

@@ -263,7 +263,7 @@ async def process_response_async(
             raw_response=response,
         )
 
-    if isinstance(response_model, ParallelBase):
+    if inspect.isclass(response_model) and issubclass(response_model, ParallelBase):
         logger.debug(f"Returning model from ParallelBase")
         model._raw_response = response
         return model
@@ -381,7 +381,7 @@ class to parse the response into. Special DSL types supported:
             raw_response=response,
         )
 
-    if isinstance(response_model, ParallelBase):
+    if inspect.isclass(response_model) and issubclass(response_model, ParallelBase):
         logger.debug(f"Returning model from ParallelBase")
         model._raw_response = response
         return model