Support multi channel input

[kmzzhang]

The featurizer input needs to support a list of featurizer configs
NBI also need to support simulator outputs of type list where each element is fed into the corresponding featurizer

[jackieblaum]

class multi(nn.Module):
def init(self.list_of_nets)"
self.nets = list_of_nets
self.n_net = len(list_of_nets)
def forward(self, list_of_x):
out = list()
for i in range(self.n_net):
out.append(self.neti)
return torch.cat(out)

Also in nbi.engine the functions scale_x and should also allow for multi channel input

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kz