Observation Descriptor
@Serializable
One declared observation: what a rule may read, and what the ith entry of an observation vector means. Order is significant — the position in the descriptor's list is the position in the array (§4.2.3).
unit is optional and unverifiable. The library cannot check that a quantity declared in "jobs" is not really in server-units, and says so plainly; what it can do is carry the declaration where a rule can compare it against what the rule was written for and refuse (§4.2.4).