input: Write a function to create an Employee class and a method to display employee details.
  assert emp1.show_details() == "Employee Details\n-------------------------------\nName: John\nAge: 25\nSalary: 10000\nDesignation: Developer"
  emp2 = Employee("Jane", 30, 15000, "Manager")
  assert emp2.show_details() == "Employee Details\n-------------------------------\nName: Jane\nAge: 30\nSalary: 15000\nDesignation: Manager"
output: def create_employee_class():
      class Employee:
          def __init__(self, name, age, salary, designation):
              self.name = name
              self.age = age
              self.salary = salary
              self.designation = designation
  
          def show_details(self):
              return f"Employee Details\n-------------------------------\nName: {self.name}\nAge: {self.age}\nSalary: {self.salary}\nDesignation: {self.designation}"
  
      return Employee
  
  Employee = create_employee_class()
  emp1 = Employee("John", 25, 10000, "Developer")