Normalize demucs/maml behavior when using get_module

[jansel]

I am doing some tests where I iterate over benchmarks and do some automated changes and output correctness checking. This is a minor change to normalize the behavior of these two benchmarks.

First I make them return a Tensor() (to make checking outputs easier). Before they returned None/np.ndarray.

Second I make the following do inference (for maml it actually did training):

module, example_inputs = benchmark.get_module()
module.eval()(*example_inputs)