System validation module

[tsmbland]

Currently it's very easy to create a system that's inappropriate for the way that MUSE works, which can lead to nonsense results, and there are very few checks in place to prevent this.

Examples:

• If multiple sectors have the same output commodity, and these sectors have the same priority, each sector will match demand independently, and so overall supply will be double what's required

• Spiraling prices when a commodity is both an input and an output to a technology. More generally, I think the system needs to be a directed acyclic graph (ie. a linear flow of commodities from primary commodities to service demands, without any cycles).

• The priority of the sectors needs to be set up appropriately so that each sector is solved before any other sector it receives commodities from

Very rough idea at the moment, but I think the first step would be to build the system as a graph, and then there are several checks that can be performed on this graph to make sure it's structured appropriately