add some more caching around the state file & geometry calculations

able to process a simulation in ~2 seconds in the optimistic path

src/render.rs

@@ -561,6 +561,8 @@ impl<S: SampleableSim> Renderer<S> for MultiRenderer<S> {
 #[derive(Serialize, Deserialize)]
 pub struct SerializedFrame<S=StaticSim> {
     pub state: S,
+    /// although not generally necessary to load the sim, saving the measurements is beneficial for
+    /// post-processing.
     pub measurements: Vec<Box<dyn AbstractMeasurement>>,
 }
 
@@ -588,8 +590,8 @@ impl SerializerRenderer {
         }
     }
 
-    /// Same as `new`, but cast to StaticSim before serializing. This tends to result in a smaller
-    /// file.
+    /// Same as `new`, but cast to StaticSim before serializing. This yields a file that's easier
+    /// for post-processing, and may be smaller in size.
     pub fn new_static(fmt_str: &str) -> Self {
         Self {
             fmt_str: fmt_str.into(),