instrument the stimulus evaluation in our sim

... stimulus evaluation accounts for like 80% of the execution time 🤦

crates/coremem/src/sim/mod.rs

@@ -1,3 +1,4 @@
+use crate::diagnostics::SyncDiagnostics;
 use crate::geom::{Coord, Cube, Index, InvertedRegion, Region};
 use crate::cross::mat::{FullyGenericMaterial, Material, Vacuum};
 use crate::cross::real::Real;
@@ -209,6 +210,9 @@ pub trait AbstractSim: Sync {
     /// Take a "snapshot" of the simulation, dropping all material-specific information.
     fn to_static(&self) -> StaticSim;
     fn to_generic(&self) -> GenericSim<Self::Real>;
+    fn use_diagnostics(&mut self, _diag: SyncDiagnostics) {
+        // optional
+    }
 
 
     //--- HELPER METHODS below (derived) ---//