include all the changes into the code. print every line

code:
// Define a trait for common characteristics of entities in the shop
trait Identifiable {
  val id: Int
}

trait Nameable {
  val name: String
}

// Define a trait for behavior of entities that can be displayed
trait Displayable {
  def display(): Unit
}

// Define a trait for inventory management
trait InventoryManagement {
  def checkStock(): Unit
  def updateStock(amount: Int): Unit
}

// Product class with characteristics and behaviors
case class Product(id: Int, name: String, price: Double, stock: Int) extends Identifiable with Nameable with InventoryManagement {
  override def checkStock(): Unit = ???
  override def updateStock(amount: Int): Unit = ???
}

// User class with characteristics
case class User(id: Int, name: String, email: String) extends Identifiable with Nameable with UserOperations {
  override def login(): Unit = ???
  override def logout(): Unit = ???
}


// Define a trait for operations that can be performed by users
trait UserOperations {
  def login(): Unit
  def logout(): Unit
}

// Order class with characteristics and behaviors
case class Order(id: Int, userId: Int, productIds: List[Int], totalAmount: Double) extends Identifiable {
  def calculateTotal(): Unit = ???
}

// Define a trait for managing orders
trait OrderManagement {
  def placeOrder(order: Order): Unit
  def cancelOrder(orderId: Int): Unit
  def updateOrder(order: Order): Unit
  def viewOrder(orderId: Int): Order
}


// ShoppingCart class to hold products
case class ShoppingCart(products: List[Product]) {
  def addProduct(product: Product): Unit = ???
  def removeProduct(productId: Int): Unit = ???
}

// Singleton object for the shop
object StationeryShop extends Displayable with OrderManagement {
  var products: List[Product] = List()
  var users: List[User] = List()
  var orders: List[Order] = List()

  override def display(): Unit = ???
  override def placeOrder(order: Order): Unit = ???
  override def cancelOrder(orderId: Int): Unit = ???
}

// Companion objects for each class can serve as factories and contain static methods
object Product {
  def apply(id: Int, name: String, price: Double, stock: Int): Product = new Product(id, name, price, stock)
}

object User {
  def apply(id: Int, name: String, email: String): User = new User(id, name, email)
}

object Order {
  def apply(id: Int, userId: Int, productIds: List[Int], totalAmount: Double): Order = new Order(id, userId, productIds, totalAmount)
}

changes:
UserOperations Trait: Currently, the UserOperations trait is defined but not used. You could consider having the User class extend this trait. This would provide behaviors such as login and logout to the User class. Here’s how you could do it:
Scala

case class User(id: Int, name: String, email: String) extends Identifiable with Nameable with UserOperations {
  override def login(): Unit = ???
  override def logout(): Unit = ???
}

Displayable Trait: The Displayable trait is only used in the StationeryShop singleton object. You could consider using it in other classes as well, such as Product, User, and Order, to display their details. Here’s an example for the Product class:
Scala

case class Product(id: Int, name: String, price: Double, stock: Int) extends Identifiable with Nameable with InventoryManagement with Displayable {
  override def checkStock(): Unit = ???
  override def updateStock(amount: Int): Unit = ???
  override def display(): Unit = ???
}

OrderManagement Trait: The OrderManagement trait is defined and used in the StationeryShop singleton object. You could consider creating a separate OrderManager class that extends this trait. This would separate the concerns of managing orders from the StationeryShop object. Here’s how you could do it:
Scala

case class OrderManager() extends OrderManagement {
  override def placeOrder(order: Order): Unit = ???
  override def cancelOrder(orderId: Int): Unit = ???
  override def updateOrder(order: Order): Unit = ???
  override def viewOrder(orderId: Int): Order = ???
}

include the Displayable trait in all the classes. This would mean that every class would need to implement the display method, which could be used to print or display the details of the object. Here’s how you could do it:

Scala

// Product class with characteristics and behaviors
case class Product(id: Int, name: String, price: Double, stock: Int) extends Identifiable with Nameable with InventoryManagement with Displayable {
  override def checkStock(): Unit = ???
  override def updateStock(amount: Int): Unit = ???
  override def display(): Unit = ???
}

// User class with characteristics and behaviors
case class User(id: Int, name: String, email: String) extends Identifiable with Nameable with UserOperations with Displayable {
  override def login(): Unit = ???
  override def logout(): Unit = ???
  override def display(): Unit = ???
}

// Order class with characteristics and behaviors
case class Order(id: Int, userId: Int, productIds: List[Int], totalAmount: Double) extends Identifiable with Displayable {
  def calculateTotal(): Unit = ???
  override def display(): Unit = ???
}

// ShoppingCart class to hold products
case class ShoppingCart(products: List[Product]) extends Displayable {
  def addProduct(product: Product): Unit = ???
  def removeProduct(productId: Int): Unit = ???
  override def display(): Unit = ???
}

// Singleton object for the shop
object StationeryShop extends Displayable with OrderManagement {
  var products: List[Product] = List()
  var users: List[User] = List()
  var orders: List[Order] = List()

  override def display(): Unit = ???
  override def placeOrder(order: Order): Unit = ???
  override def cancelOrder(orderId: Int): Unit = ???
}

Remember, the display method in each class should be implemented to display the details of the object in a way that makes sense for that class. For example, for the Product class, it could display the product’s id, name, price, and stock. For the User class, it could display the user’s id, name, and email.