implement base_url prop method for OpenAIResponsesModel

Author: chasefarmer-pixee

pydantic_ai_slim/pydantic_ai/models/openai.py

@@ -948,6 +948,10 @@ def __init__(
 
         super().__init__(settings=settings, profile=profile or provider.model_profile)
 
+    @property
+    def base_url(self) -> str:
+        return str(self.client.base_url)
+
     @property
     def model_name(self) -> OpenAIModelName:
         """The model name."""