example1

题目需求（逐条实现）

1️⃣ 找出工资高于 8000 的员工​ 2️⃣ 按部门分组，统计每个部门的 平均薪资​ 3️⃣ 找出每个部门工资最高的员工​ 4️⃣ 得到所有员工工资的求和​ 5️⃣ 找出平均工资最高的部门

# 测试数据
List<Employee> employees = List.of(
    new Employee(1, "Alice", "IT", 12000, 28),
    new Employee(2, "Bob", "IT", 9000, 35),
    new Employee(3, "Charlie", "HR", 7000, 26),
    new Employee(4, "David", "HR", 11000, 40),
    new Employee(5, "Eve", "Finance", 15000, 32)
);