[bug] `KVStorageManager._merge_tensors_to_tensordict` cannot merge NPU tensors to a nested tensor

[dpj135]

Description

NPU tensors will be NonTensorStack! Because torch.nested.as_nested_tensor() does not support NPU tensors.

  try:
      return field, torch.nested.as_nested_tensor(chunk, layout=torch.jagged)
  except (RuntimeError, TypeError):
      try:
          return field, torch.nested.as_nested_tensor(chunk, layout=torch.strided)
      except (RuntimeError, TypeError):
          return field, NonTensorStack(*chunk)