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/jump.rs

@@ -2,10 +2,17 @@ use bevy::prelude::*;
 
 use crate::{
     fighter::{
-        animation::AnimKind, state::{
-            CollisionContext, EnterContext, FighterState, FighterStateImpl, InterruptContext, UpdateContext, air::{self, AirborneStateCommon}, air_dodge::{self, AirDodgeState}, ground::{self, GroundedStateCommon},
+        animation::AnimKind,
+        state::{
+            CollisionContext, EnterContext, FighterState, FighterStateImpl, InterruptContext,
+            UpdateContext,
+            air::{self, AirborneStateCommon},
+            air_dodge::{self, AirDodgeState},
+            ground,
         },
-    }, input::FighterCommands, math::{int::FGi32, vec::FGVec2},
+    },
+    input::FighterCommands,
+    math::{int::FGi32, vec::FGVec2},
 };
 #[derive(Debug, Hash, Clone, Copy)]
 pub enum JumpType {
@@ -22,14 +29,12 @@ pub struct JumpState {
 
 #[derive(Debug, Clone, Hash)]
 pub struct JumpSquatState {
-    pub grounded_common: GroundedStateCommon,
     pub duration_counter: u32,
 }
 
 impl JumpSquatState {
-    pub fn create(grounded_common: GroundedStateCommon) -> Self {
+    pub fn create() -> Self {
         Self {
-            grounded_common,
             duration_counter: 0,
         }
     }
@@ -69,7 +74,10 @@ impl FighterStateImpl for JumpSquatState {
             } else {
                 JumpType::ShortHop
             };
-            Some(FighterState::Jump(JumpState { jump_type, airborne_state_common: AirborneStateCommon::default() }))
+            Some(FighterState::Jump(JumpState {
+                jump_type,
+                airborne_state_common: AirborneStateCommon::default(),
+            }))
         } else {
             None
         }
@@ -84,17 +92,15 @@ impl FighterStateImpl for JumpSquatState {
         &mut self,
         state_context: &mut CollisionContext,
     ) -> Option<FighterState> {
-        ground::collision_interrupt(state_context, &mut self.grounded_common, false)
+        ground::collision_interrupt(state_context, false)
     }
 
     fn on_enter(&mut self, state_context: &mut EnterContext) {
         state_context.play_animation(AnimKind::JumpSquat, false);
         state_context.input.clear_command(FighterCommands::Jump);
     }
-    
-    fn is_visually_grounded<'a>(
-        &'a self,
-    ) -> bool {
+
+    fn is_visually_grounded<'a>(&'a self) -> bool {
         true
     }
 }
@@ -105,7 +111,7 @@ impl FighterStateImpl for JumpState {
         if state_context.input.has_command(FighterCommands::Jump) {
             Some(FighterState::Jump(JumpState {
                 jump_type: JumpType::DoubleJump,
-                airborne_state_common: AirborneStateCommon::default()
+                airborne_state_common: AirborneStateCommon::default(),
             }))
         } else {
             air_dodge::check_input(state_context)
@@ -176,22 +182,17 @@ impl FighterStateImpl for JumpState {
             crate::fighter::state::land::LandingType::Normal,
         )
     }
-    
-    fn is_visually_grounded<'a>(
-        &'a self,
-    ) -> bool {
+
+    fn is_visually_grounded<'a>(&'a self) -> bool {
         false
     }
 }
 
-pub fn check_input(
-    state_context: &InterruptContext,
-    ground_common: &GroundedStateCommon,
-) -> Option<FighterState> {
+pub fn check_input(state_context: &InterruptContext) -> Option<FighterState> {
     state_context
         .input
         .has_command(FighterCommands::Jump)
-        .then(|| FighterState::JumpSquat(JumpSquatState::create(ground_common.clone())))
+        .then(|| FighterState::JumpSquat(JumpSquatState::create()))
 }
 
 pub fn check_input_double_jump(state_context: &InterruptContext) -> Option<FighterState> {
@@ -201,7 +202,7 @@ pub fn check_input_double_jump(state_context: &InterruptContext) -> Option<Fight
         .then(|| {
             FighterState::Jump(JumpState {
                 jump_type: JumpType::DoubleJump,
-                airborne_state_common: AirborneStateCommon::default()
+                airborne_state_common: AirborneStateCommon::default(),
             })
         })
 }