Stop validators from equivocating on reboot

Part of https://github.com/serai-dex/serai/issues/345.

The lack of full DB persistence does mean enough nodes rebooting at the same
time may cause a halt. This will prevent slashes.

Cargo.lock

@@ -9105,6 +9105,7 @@ dependencies = [
  "hex",
  "log",
  "parity-scale-codec",
+ "serai-db",
  "thiserror",
  "tokio",
 ]