fix(anthropic.py): support async claude 3 tool calling + streaming

https://github.com/BerriAI/litellm/issues/2644

litellm/llms/anthropic.py

@@ -301,7 +301,7 @@ def completion(
                 )
                 streaming_choice.delta = delta_obj
                 streaming_model_response.choices = [streaming_choice]
-                completion_stream = model_response_iterator(
+                completion_stream = ModelResponseIterator(
                     model_response=streaming_model_response
                 )
                 print_verbose(
@@ -330,8 +330,30 @@ def completion(
         return model_response
 
 
-def model_response_iterator(model_response):
-    yield model_response
+class ModelResponseIterator:
+    def __init__(self, model_response):
+        self.model_response = model_response
+        self.is_done = False
+
+    # Sync iterator
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        if self.is_done:
+            raise StopIteration
+        self.is_done = True
+        return self.model_response
+
+    # Async iterator
+    def __aiter__(self):
+        return self
+
+    async def __anext__(self):
+        if self.is_done:
+            raise StopAsyncIteration
+        self.is_done = True
+        return self.model_response
 
 
 def embedding():