fix(openai): disable stream_usage in chat completions if OPENAI_BASE_URL is set (#33298)

This env var is used internally by the OpenAI client.

libs/partners/openai/langchain_openai/chat_models/base.py

@@ -776,7 +776,8 @@ class BaseChatOpenAI(BaseChatModel):
         self.openai_api_base = self.openai_api_base or os.getenv("OPENAI_API_BASE")
 
         # Enable stream_usage by default if using default base URL and client
-        if all(
+        if (
+            all(
                 getattr(self, key, None) is None
                 for key in (
                     "stream_usage",
@@ -790,6 +791,8 @@ class BaseChatOpenAI(BaseChatModel):
                     "http_client",
                     "http_async_client",
                 )
+            )
+            and "OPENAI_BASE_URL" not in os.environ
         ):
             self.stream_usage = True