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/air_dodge.rs

@@ -1,9 +1,16 @@
 use crate::{
     fighter::{
-        animation::AnimKind, state::{
-            CollisionContext, EnterContext, FighterState, FighterStateImpl, InterruptContext, UpdateContext, air::{self, AirborneStateCommon}, fall::FallState, land::LandingType,
+        animation::AnimKind,
+        state::{
+            CollisionContext, EnterContext, FighterState, FighterStateImpl, InterruptContext,
+            UpdateContext,
+            air::{self, AirborneStateCommon},
+            fall::FallState,
+            land::LandingType,
         },
-    }, input, math::vec::FGVec2,
+    },
+    input,
+    math::vec::FGVec2,
 };
 
 #[derive(Debug, Clone, Hash)]
@@ -16,7 +23,9 @@ impl FighterStateImpl for AirDodgeState {
 
     fn check_interrupt(&self, state_context: &mut InterruptContext) -> Option<FighterState> {
         if state_context.is_current_animation_finished() {
-            Some(FighterState::Fall(FallState::new(AirborneStateCommon::default())))
+            Some(FighterState::Fall(FallState::new(
+                AirborneStateCommon::default(),
+            )))
         } else {
             None
         }
@@ -29,6 +38,7 @@ impl FighterStateImpl for AirDodgeState {
             state_context.velocity,
             state_context.translation,
             state_context.prev_translation,
+            state_context.surface,
         );
     }
 
@@ -45,10 +55,8 @@ impl FighterStateImpl for AirDodgeState {
         state_context.velocity.0 =
             self.direction * state_context.fighter_attributes.air_dodge_velocity;
     }
-    
-    fn is_visually_grounded<'a>(
-        &'a self,
-    ) -> bool {
+
+    fn is_visually_grounded<'a>(&'a self) -> bool {
         false
     }
 }