Implement a 'SerializerRenderer' output format

It's CBOR, which seems to pack not so efficiently (250*250*20 * 12
floats takes 400 MB per frame, whereas this many doubles could pack into
120 MB). serde_cbor also seems to be extremely slow: taking multiple
minutes per frame. This could be parallelized to be less problematic
though (it already is -- just bump the parallelism).

Might be worth testing other formats.

src/render.rs

@@ -462,3 +462,24 @@ impl Renderer for MultiRenderer {
         }
     }
 }
+
+pub struct SerializerRenderer {
+    out_base: String
+}
+
+impl SerializerRenderer {
+    pub fn new(out_base: &str) -> Self {
+        Self {
+            out_base: out_base.into(),
+        }
+    }
+}
+
+impl Renderer for SerializerRenderer {
+    fn render(&self, state: &dyn GenericSim, measurements: &[Box<dyn AbstractMeasurement>]) {
+        let snap = state.to_static();
+        let name = format!("{}{}.cbor", self.out_base, snap.step_no());
+        let out = File::create(name).unwrap();
+        serde_cbor::to_writer(out, &snap).unwrap();
+    }
+}