Allow ABLPInputNodes to be "homogeneous"

[kmontemayor2-sc]

Based off https://github.com/Snapchat/GiGL/pull/485/changes#r2823871652

We should probably allow anchor_node_type to be None and the labels to be straight Tensor. We'd need to do some conversion under the hood, which I'm concerned would make our code more complicated, sadly :/