refactor: extract message enum

src/msg.rs

@@ -0,0 +1,9 @@
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum Message {
+  Tick,
+  ToggleRunning,
+  ToggleMode,
+  Reset,
+  ToggleHelp,
+  Quit,
+}