Build a system for pushed, low-frequency variables

[JonnyOThan]

Many variables are things that don't change often, and could be pushed into the variable cache on edge-triggered events. Action group states, stage number, resource max levels, target properties, etc.

In addition, certain variables should only be conditionally updated, like all the maneuver node variables should only update if you have a maneuver node, target properties if you have a target, etc.