Fix memory leak in pools (#8415)

core/src/mindustry/entities/Damage.java

@@ -618,7 +618,7 @@ public class Damage{
         return Math.max(damage - armor, minArmorDamage * damage);
     }
 
-    public static class Collided{
+    public static class Collided implements Pool.Poolable{
         public float x, y;
         public Teamc target;
 
@@ -628,5 +628,10 @@ public class Damage{
             this.target = target;
             return this;
         }
+        
+        @Override
+        public void reset(){
+            target = null;
+        }
     }
 }