CheckVertex ensures that subsystem needs are satisfied (and updates them) and if so, includes the resource type in the count.

getResourceNeeds flattens a resource requirement into names This is intended to just check subsystem metadata for one resource type (e.g., node) before we have dived into a slot.

getSlotNeeds converts the string values into SlotNeeds unlike ResourceNeeds, for a slot we also have a counter for different types, and the total number we have found so far.