Fix: Change LongestArithmeticSubsequence class visibility to public

Author: Abhi13shek

src/main/java/com/thealgorithms/dynamicprogramming/LongestArithmeticSubsequence.java

@@ -3,7 +3,7 @@
 import java.util.HashMap;
 
 @SuppressWarnings({ "rawtypes", "unchecked" })
-final class LongestArithmeticSubsequence {
+public final class LongestArithmeticSubsequence {
     private LongestArithmeticSubsequence() {
     }