feat: Add option to input array with payoffs

[eliotwrobson]

In certain situations, it can be desirable to give a scaling factor per-node when computing the influence of a certain seed set (i.e., if a certain node is activated, we want to give it a higher weight than another node). Allow model classes to take in a scaling factor to add to a node if it is activated. This can be a more general linear function as well. Should allow faster computation of influence in certain use cases.