feat: Implement thread-safe Counter with synchronization, correct thread join logic, and add verification log file.

Author: liudmylabiletska

src/main/java/core/basesyntax/Counter.java

@@ -12,7 +12,7 @@ public Counter(int value) {
         this.value = value;
     }
 
-    public void decreaseValue() {
+    public synchronized void decreaseValue() {
         logger.info(String.format(MESSAGE,
                 "Before decrementing", Thread.currentThread().getName(), value));
         value--;

src/main/java/core/basesyntax/Main.java

@@ -3,6 +3,7 @@
 public class Main {
     public static void main(String[] args) {
         Counter counter = new Counter(20);
+
         for (int i = 1; i <= 20; i++) {
             new MyThread(counter, String.valueOf(i)).start();
         }