meas: Energy: allow non-meas code to query a simulation's energy

this is especially useful in test

crates/coremem/src/meas.rs

@@ -615,7 +615,7 @@ impl Energy {
             region: Box::new(region),
         }
     }
-    fn data<S: AbstractSim>(&self, state: &S) -> f32 {
+    pub(crate) fn data<S: AbstractSim>(&self, state: &S) -> f32 {
         // Potential energy stored in a E/M field:
         //   https://en.wikipedia.org/wiki/Magnetic_energy
         //   https://en.wikipedia.org/wiki/Electric_potential_energy#Energy_stored_in_an_electrostatic_field_distribution