Fix: mark utility classes as final for Checkstyle compliance

Author: enqneres

src/main/java/com/thealgorithms/compression/ArithmeticCoding.java

@@ -7,7 +7,7 @@
  * Reference: https://en.wikipedia.org/wiki/Arithmetic_coding
  */
 
-public class ArithmeticCoding {
+public final class ArithmeticCoding {
 
     private ArithmeticCoding() {
         throw new UnsupportedOperationException("Utility class");

src/main/java/com/thealgorithms/compression/LZW.java

@@ -10,7 +10,7 @@
  * Reference: https://en.wikipedia.org/wiki/Lempel–Ziv–Welch
  */
 
-public class LZW {
+public final class LZW {
 
     private LZW() {
         throw new UnsupportedOperationException("Utility class");