network free solvers

[isaacsas]

@TorkelE pointed out that on a multisite phosphorylation benchmark where species can have many phosphorylation states, we are starting to lose performance relative to network-free methods as the number of sites increases (NF methods track individual molecules and their states). It would be worth thinking about how to include such solvers / representations here too, especially in ways that can exploit our current SSA infrastructure.

@TorkelE when you are able to share, could you link the network files and sources?