meas: add a missing unit to the Energy measurement

crates/coremem/src/meas.rs

@@ -645,8 +645,8 @@ impl<S: AbstractSim> AbstractMeasurement<S> for Energy {
     fn key_value(&self, state: &S) -> Vec<Measurement> {
         let e = self.data(state);
         vec![
-            Measurement::new_unitless(
-                &format!("U({})", self.name), e
+            Measurement::new(
+                &format!("U({})", self.name), e, "J"
             )
         ]
     }