feat: update structure

cs2030s/labs/PE1/Sequeue.java

@@ -0,0 +1,12 @@
+public class Sequeue<T> extends Pair<T, Queueable<T>> implements Queueable {
+
+    public Sequeue(T fst, Queueable<T> snd) {
+        super(fst, snd);
+        // TODO Auto-generated constructor stub
+    }
+
+    public enq(T e) {
+        return new Sequeue<>(getFst(), getSnd().enq(e));
+    }
+
+}