fix: improve test for polygonal region containment of cuboid

- Possibly fixes #2265

worldedit-core/src/main/java/com/sk89q/worldedit/regions/Polygonal2DRegion.java

@@ -506,26 +506,28 @@ public class Polygonal2DRegion extends AbstractRegion implements FlatRegion {
     //FAWE start
     @Override
     public boolean containsEntireCuboid(int bx, int tx, int by, int ty, int bz, int tz) {
+        for (int y : new int[]{by, ty}) {
             for (int x = bx; x <= tx; x++) {
-            if (!contains(x, 0, bz)) {
+                if (!contains(x, y, bz)) {
                     return false;
                 }
             }
             for (int x = bx; x <= tx; x++) {
-            if (!contains(x, 0, tz)) {
+                if (!contains(x, y, tz)) {
                     return false;
                 }
             }
             for (int z = bz; z <= tz; z++) {
-            if (!contains(bx, 0, z)) {
+                if (!contains(bx, y, z)) {
                     return false;
                 }
             }
             for (int z = bz; z <= tz; z++) {
-            if (!contains(tx, 0, z)) {
+                if (!contains(tx, y, z)) {
                     return false;
                 }
             }
+        }
         return true;
     }
     //FAWE end

worldedit-core/src/main/java/com/sk89q/worldedit/regions/Region.java

@@ -42,8 +42,6 @@ import com.sk89q.worldedit.world.World;
 import javax.annotation.Nullable;
 import java.util.List;
 import java.util.Set;
-import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.Future;
 
 /**
  * Represents a physical shape.