Add ceiling to NumberInterface and the two numbers that implement it.

src/main/java/org/nwapw/abacus/number/NaiveNumber.java

@@ -93,6 +93,11 @@ public class NaiveNumber implements NumberInterface {
         return this.compareTo(ZERO);
     }
 
+    @Override
+    public int ceiling() {
+        return (int) Math.ceil(value);
+    }
+
     @Override
     public NumberInterface promoteTo(Class<? extends NumberInterface> toClass) {
         if (toClass == this.getClass()) return this;