fix: apply code review suggestions

Apply reviewer suggestions from PR review.

Author: giulio-leone

src/openai/lib/streaming/responses/_responses.py

@@ -113,8 +113,10 @@ def cancel(self) -> Response:
         if response_id is None:
             raise ValueError("Cannot cancel: response ID not yet available. Wait for the first event.")
         if self._cancel_response is None:
-            raise ValueError("Cancel not available for this stream.")
-        self.close()
+        try:
+            result = self._cancel_response(response_id)
+        finally:
+            self.close()
         try:
             return self._cancel_response(response_id)
         except Exception:
@@ -242,8 +244,10 @@ async def cancel(self) -> Response:
         to cancel the response.
 
         Returns the cancelled Response object.
-        """
-        response_id = self.response_id
+        try:
+            result = await self._cancel_response(response_id)
+        finally:
+            await self.close()
         if response_id is None:
             raise ValueError("Cannot cancel: response ID not yet available. Wait for the first event.")
         if self._cancel_response is None: