BUGFIX: Torus: don't normalize the cross section normal

this would have led to incorrectly scaled current measurements
(but not incorrect current generation). we were likely severely
over-estimating the current.

crates/coremem/src/geom/region/mod.rs

@@ -20,7 +20,7 @@ dyn_clone::clone_trait_object!(Region);
 
 /// some (volume) which has a tangent vector everywhere inside/on it.
 /// for example, a cylinder has tangents everywhere except its axis.
-/// the return vector should be normalized, or zero.
+/// the returned vector should represent the area of the cross section.
 pub trait HasCrossSection {
     fn cross_section_normal(&self, p: Meters) -> Vec3<f32>;
 }

crates/coremem/src/geom/region/primitives.rs

@@ -109,7 +109,7 @@ impl HasCrossSection for Torus {
         let axis = self.axis();
         let to_coord = *coord - *self.center();
         // this creates a normal which always points "counter-clockwise" along the shape
-        axis.cross(to_coord).norm()
+        axis.cross(to_coord)
     }
 }