refactor: extract updateAutoAttack() from update()

Move 98 lines of auto-attack leash range, melee resync, facing
alignment, and hostile attacker orientation into a dedicated method.
update() is now ~180 lines (74% reduction from original 704).

include/game/game_handler.hpp

@@ -2318,6 +2318,7 @@ public:
     void updateTimers(float deltaTime);
     void updateEntityInterpolation(float deltaTime);
     void updateTaxiAndMountState(float deltaTime);
+    void updateAutoAttack(float deltaTime);
 
     /**
      * Reset DBC-backed caches so they reload from new expansion data.