fix: add missing __aiter__ method to ResponseStream for async iteration support

The ResponseStream class was missing the __aiter__ method which is required
for async iteration with 'async for' loops. This caused TypeError when trying
to iterate over streaming responses asynchronously.

Added __aiter__ method that returns self, following the standard async iterator
protocol pattern.

Author: rtyer

packages/opentelemetry-instrumentation-openai/opentelemetry/instrumentation/openai/v1/responses_wrappers.py

@@ -302,6 +302,9 @@ async def __aexit__(self, exc_type, exc_val, exc_tb):
     def __iter__(self):
         return self
 
+    def __aiter__(self):
+        return self
+
     def __next__(self):
         try:
             chunk = self.__wrapped__.__next__()