Make sure policies don't mutate the batch (#323)

lerobot/common/policies/tdmpc/modeling_tdmpc.py

@@ -137,6 +137,7 @@ class TDMPCPolicy(nn.Module, PyTorchModelHubMixin):
     def select_action(self, batch: dict[str, Tensor]) -> Tensor:
         """Select a single action given environment observations."""
         batch = self.normalize_inputs(batch)
+        batch = dict(batch)  # shallow copy so that adding a key doesn't modify the original
         batch["observation.image"] = batch[self.input_image_key]
 
         self._queues = populate_queues(self._queues, batch)
@@ -316,6 +317,7 @@ class TDMPCPolicy(nn.Module, PyTorchModelHubMixin):
         device = get_device_from_parameters(self)
 
         batch = self.normalize_inputs(batch)
+        batch = dict(batch)  # shallow copy so that adding a key doesn't modify the original
         batch["observation.image"] = batch[self.input_image_key]
         batch = self.normalize_targets(batch)