fix(ml): armnn not being used (#10929)

* fix armnn not being used, move fallback handling to main, add tests

* formatting

machine-learning/app/conftest.py

@@ -168,6 +168,12 @@ def warning() -> Iterator[mock.Mock]:
         yield mocked
 
 
+@pytest.fixture(scope="function")
+def exception() -> Iterator[mock.Mock]:
+    with mock.patch.object(log, "exception") as mocked:
+        yield mocked
+
+
 @pytest.fixture(scope="function")
 def snapshot_download() -> Iterator[mock.Mock]:
     with mock.patch("app.models.base.snapshot_download") as mocked: