add backend handling

custom_st.py

@@ -26,9 +26,15 @@ class Transformer(nn.Module):
         processor_args: Optional[Dict[str, Any]] = None,
         cache_dir: Optional[str] = None,
         device: str = 'cuda:0',
+        backend: Literal['torch', 'onnx', 'openvino'] = 'torch',
         **kwargs,
     ) -> None:
         super(Transformer, self).__init__()
+
+        if backend != 'torch':
+            raise ValueError(
+                f'Backend \'{backend}\' is not supported, please use \'torch\' instead'
+            )
         
         self.device = device
         self.dimension = dimension