Fix ledge transitions and root motion loops (#91)

## Summary

- resolve each ledge action to the walkable segment on the stage-interior side
- preserve repeating root-motion displacement across every animation cycle
- add regression coverage for left/right ledge segments and multiple root-motion wraps
- Implement ledge intangibility

Reviewed-on: #91
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/game_settings.rs

@@ -52,6 +52,7 @@ pub struct FighterSettingsCommon {
     pub intangible_pulse_duration: u32,
 
     pub angel_platform_invulnerability_duration: u32,
+    pub ledge_grab_invulnerability_duration: u32,
 
     /// When hit while the receiver is in the air, use this angle
     pub sakurai_angle_aerial_angle: FGi32,