feat: refactor SavingsAccount class to extend CheckingAccount with updated package structure

Author: nia-source

lesson_17/bank/bank_app/src/main/java/com/codedifferently/lesson17/SavingsAccount.java

@@ -0,0 +1,13 @@
+package com.codedifferently.lesson17.bank;
+
+import java.util.Set;
+
+/**
+ * Represents a savings account that does not support check writing.
+ */
+public class SavingsAccount extends CheckingAccount {
+
+    public SavingsAccount(String accountNumber, Set<Customer> owners, double initialBalance) {
+        super(accountNumber, owners, initialBalance);
+    }
+}