Add authoritative fighter surface state (#60)

## Summary
- add a rollback-tracked `FighterSurfaceState` as the single source of truth for stage contact
- move active stage line ownership out of individual grounded fighter states
- update landing, airborne motion, ledge departure, hit reactions, and debug save states to maintain surface contact
- add tests for contact lifecycle, connected-segment traversal, and ledge departure

Reviewed-on: #60
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/fighter/state/dash.rs

@@ -5,52 +5,43 @@ use super::{
 use crate::fighter::FighterFacingDirection;
 use crate::fighter::animation::AnimKind;
 use crate::fighter::state::FighterState;
-use crate::fighter::state::ground::GroundedStateCommon;
 use crate::input::FighterCommands::{SmashMoveLeft, SmashMoveRight};
 
 #[derive(Debug, Clone, Hash)]
 pub struct DashState {
     direction: FighterFacingDirection,
-    pub ground_common: GroundedStateCommon,
 }
 
 impl DashState {
-    pub fn new(direction: FighterFacingDirection, ground_common: GroundedStateCommon) -> Self {
-        Self {
-            direction,
-            ground_common,
-        }
+    pub fn new(direction: FighterFacingDirection) -> Self {
+        Self { direction }
     }
 }
 
 impl FighterStateImpl for DashState {
     const NAME: &'static str = "Dash";
     fn check_interrupt(&self, ctx: &mut InterruptContext) -> Option<FighterState> {
-        let ground = &self.ground_common;
         let attributes = ctx.fighter_attributes;
 
         // A reverse dash can interrupt before IASA
         if let Some(direction) =
             check_smash_input_with_dir(ctx).filter(|direction| *direction != self.direction)
         {
-            return Some(FighterState::Dash(DashState::new(
-                direction,
-                ground.clone(),
-            )));
+            return Some(FighterState::Dash(DashState::new(direction)));
         }
 
-        if let Some(state) = ground::grounded_movement_common_interrupts(ctx, ground) {
+        if let Some(state) = ground::grounded_movement_common_interrupts(ctx) {
             return Some(state);
         }
 
         if ctx.is_current_animation_finished() {
-            return run::check_input(ctx, ground)
-                .or_else(|| walk::check_input(ctx, ground))
-                .or_else(|| wait::check_input(ctx, ground));
+            return run::check_input(ctx)
+                .or_else(|| walk::check_input(ctx))
+                .or_else(|| wait::check_input(ctx));
         }
 
         if ctx.get_current_animation_frame() > attributes.dash_acceleration_duration {
-            return run::check_input(ctx, ground);
+            return run::check_input(ctx);
         }
 
         None
@@ -106,12 +97,10 @@ impl FighterStateImpl for DashState {
         &mut self,
         state_context: &mut CollisionContext,
     ) -> Option<FighterState> {
-        ground::collision_interrupt(state_context, &mut self.ground_common, true)
+        ground::collision_interrupt(state_context, true)
     }
-    
-    fn is_visually_grounded<'a>(
-        &'a self,
-    ) -> bool {
+
+    fn is_visually_grounded<'a>(&'a self) -> bool {
         true
     }
 }
@@ -126,10 +115,6 @@ fn check_smash_input_with_dir(state_context: &InterruptContext) -> Option<Fighte
     }
 }
 
-pub fn check_input(
-    state_context: &InterruptContext,
-    ground_common: &GroundedStateCommon,
-) -> Option<FighterState> {
-    check_smash_input_with_dir(state_context)
-        .map(|dir| FighterState::Dash(DashState::new(dir, ground_common.clone())))
+pub fn check_input(state_context: &InterruptContext) -> Option<FighterState> {
+    check_smash_input_with_dir(state_context).map(|dir| FighterState::Dash(DashState::new(dir)))
 }