Request to allow outputs in ModelDescr to be Sequence[Sequence[OutputTensorDescr]]

[qin-yu]

Currently:

    outputs: NotEmpty[Sequence[OutputTensorDescr]]
    """Describes the output tensors."""

Cellpose's ResNet produces tuple[Tensor, Tensor, list[Tensor]]. It would be nice to support this if it only introduces little trouble, otherwise please ignore this because the list can be unpacked by who uploads the Cellpose models.