const CRATER_SHAPE: { 13 fields }
One crater's profile, as the proportions craterProfile is drawn from.
sizeFloor is the smallest crater a level places as a fraction of its
largest — diameters run over one octave inside a level. relaxSpan is how
many transition diameters the palimpsest ramp spans. Everything else is a
measured lunar proportion, named where craterProfile spends it.