Implement hitstop shake (#42)

Reviewed-on: #42
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/fighter/state/jump.rs

@@ -96,6 +96,12 @@ impl FighterStateImpl for JumpSquatState {
         state_context.play_animation(AnimKind::JumpSquat, false);
         state_context.input.clear_command(FighterCommands::Jump);
     }
+    
+    fn is_visually_grounded<'a>(
+        &'a self,
+    ) -> bool {
+        true
+    }
 }
 
 impl FighterStateImpl for JumpState {
@@ -174,6 +180,12 @@ impl FighterStateImpl for JumpState {
             crate::fighter::state::land::LandingType::Normal,
         )
     }
+    
+    fn is_visually_grounded<'a>(
+        &'a self,
+    ) -> bool {
+        false
+    }
 }
 
 pub fn check_input(