[ENH][REF] Add implementation for torch backend in the scoreboard model

[jgranley]

Support engine='torch' for the scoreboard model. This should provide an example implementation for any future torch models. The torch class should inherit from nn.module. Any other architectural details (e.g. abstract or mixin classes, changes to Model or BaseModel) should also be sorted out.

This does not need to worry at all about compiling to ONNX yet. Lets just get a torch backend working first.