Deduplicate fighter state lifecycle policies (#36)

Fixes #22

Extracts shared grounded collision/friction and airborne movement/landing policies while preserving state-specific behavior. Running fighters now pass `can_walk_off = true` so they can run off platform edges. Includes grounded and airborne hitstun call sites.

Reviewed-on: #36
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/fighter/state/hitstun.rs

@@ -6,8 +6,8 @@ use crate::{
             CollisionContext, EnterContext, ExitContext, FighterState, FighterStateImpl,
             InterruptContext, UpdateContext, air,
             fall::FallState,
-            ground::{GroundedMotionResult, GroundedStateCommon, collide_with_stage_grounded},
-            land::{LandingState, LandingType},
+            ground::{GroundedStateCommon, collision_interrupt},
+            land::LandingType,
             wait::WaitState,
         },
     },
@@ -88,29 +88,10 @@ impl FighterStateImpl for HitstunState {
     ) -> Option<FighterState> {
         match &mut self.hitstop_kind {
             HitstopStateKind::Grounded(grounded_state_common) => {
-                if let GroundedMotionResult::InAir =
-                    collide_with_stage_grounded(state_context, grounded_state_common, true)
-                {
-                    Some(FighterState::Fall(FallState {}))
-                } else {
-                    None
-                }
+                collision_interrupt(state_context, grounded_state_common, true)
             }
             HitstopStateKind::Airborne => {
-                if let Some(res) = state_context.air_collide_with_stage() {
-                    // Adjust translation
-                    state_context.translation.0 =
-                        res.hit_position - state_context.ecb.get_bottom_point();
-                    let grounded_common = GroundedStateCommon {
-                        current_line_id: res.line_id,
-                    };
-                    Some(FighterState::Land(LandingState::create(
-                        grounded_common,
-                        LandingType::Normal,
-                    )))
-                } else {
-                    None
-                }
+                air::collision_interrupt(state_context, LandingType::Normal)
             }
         }
     }