Initial work on rollback and refactor

src/input/frame.rs

@@ -0,0 +1,10 @@
+use bevy::prelude::*;
+use serde::{Deserialize, Serialize};
+
+/// One frame of a player's raw input. This is the type GGRS serializes and
+/// sends over the wire, so keep it small and keep it `PartialEq`.
+#[derive(Copy, Clone, Debug, PartialEq, Default, Serialize, Deserialize)]
+pub struct FighterInputFrame {
+    pub movement: Vec2,
+    pub directional_attack: Vec2,
+}