feat: add Lab4

Lab1/JoinCounterQueueEvent.java

@@ -0,0 +1,23 @@
+public class JoinCounterQueueEvent extends Event {
+  private Customer customer;
+  private ServiceCounter counter;
+
+  public JoinCounterQueueEvent(double time, Customer customer, ServiceCounter counter) {
+    super(time);
+    this.customer = customer;
+    this.counter = counter;
+  }
+
+  @Override
+  public Event[] simulate() {
+    this.counter.joinQueue(customer);
+    return new Event[] {};
+  }
+
+  @Override
+  public String toString() {
+    return String.format("%s: %s joined counter queue (at %s)",
+        super.toString(),
+        this.customer, this.counter);
+  }
+}