Welcome! Today, we will explore creating a simple address book application using Python dictionaries. This task will help you understand manipulating dictionaries in Python, focusing on adding, retrieving, and deleting entries. By the end of this lesson, you'll have a solid grasp of these fundamental operations.

In this task, we will implement three methods to manage our address book:

• add_contact(self, name: str, phone_number: str) -> bool: Adds a new contact. Returns False if the contact already exists, otherwise adds the contact and returns True. In this task, let's assume phone numbers do not change, so it's not allowed to overwrite the existing contact's number.
• get_contact(self, name: str) -> str | None: Retrieves the phone number for a given name. Returns None if the contact does not exist.
• delete_contact(self, name: str) -> bool: Deletes a contact with the given name. Returns True if the contact exists and is deleted, False otherwise.