Fix simulation reaching different states when started from different snaphots.

src/data/maybe_serializable_data.rs

@@ -0,0 +1,14 @@
+use downcast_rs::{impl_downcast, DowncastSync};
+#[cfg(feature = "serde-serialize")]
+use erased_serde::Serialize;
+
+/// Piece of data that may be serializable.
+pub trait MaybeSerializableData: DowncastSync {
+    /// Convert this shape as a serializable entity.
+    #[cfg(feature = "serde-serialize")]
+    fn as_serialize(&self) -> Option<(u32, &dyn Serialize)> {
+        None
+    }
+}
+
+impl_downcast!(sync MaybeSerializableData);