(refactor router.py ) - PR 3 - Ensure all functions under 100 lines (#6181)

* add flake 8 check

* split up litellm _acompletion

* fix get model client

* refactor use commong func to add metadata to kwargs

* use common func to get timeout

* re-use helper to _get_async_model_client

* use _handle_mock_testing_rate_limit_error

* fix docstring for _handle_mock_testing_rate_limit_error

* fix function_with_retries

* use helper for mock testing fallbacks

* router - use 1 func for simple_shuffle

* add doc string for simple_shuffle

* use 1 function for filtering cooldown deployments

* fix use common helper to _get_fallback_model_group_from_fallbacks

tests/local_testing/test_azure_openai.py

@@ -73,6 +73,7 @@ async def test_azure_tenant_id_auth(respx_mock: MockRouter):
         ],
         created=int(datetime.now().timestamp()),
     )
+    litellm.set_verbose = True
     mock_request = respx_mock.post(url__regex=r".*/chat/completions.*").mock(
         return_value=httpx.Response(200, json=obj.model_dump(mode="json"))
     )