[azopenaiextensions] Of course, the streaming version can throttle as well. (#23544)

* Of course, the streaming version can throttle as well.
* The listing API depends on the "after this assistant" ID existing. I was just paging over the list of assistants randomly, and that is hazardous - now I always start with a known assistant ID (my own).

sdk/ai/azopenaiextensions/client_assistants_test.go

@@ -61,6 +61,7 @@ func TestAssistants(t *testing.T) {
 	// listing assistants
 	{
 		pager, err := assistantClient.List(context.Background(), openai.BetaAssistantListParams{
+			After: openai.F(assistant.ID),
 			Limit: openai.Int(1),
 		})
 		require.NoError(t, err)

sdk/ai/azopenaiextensions/client_chat_completions_extensions_test.go

@@ -89,7 +89,7 @@ func TestChatExtensionsStreaming_extensions_bringYourOwnData(t *testing.T) {
 		}
 	}
 
-	require.NoError(t, streamer.Err())
+	customRequireNoError(t, streamer.Err())
 	require.NotEmpty(t, text)
 
 	t.Logf("Streaming content = %s", text)