Implement mutual friends computation with tests

Implement mutual friends in a friend graph. Given a User class: id currentFriends: list[User] In a new file, implement: def mutual_friends(user_a: User, user_b: User) -> list[User]: """Return the mutual friends of user_a and user_b (dedup by id).""" Requirements: Mutual friends are users present in both user_a.currentFriends and user_b.currentFriends (compare by id). Output must have no duplicates. Any order is acceptable, but document your ordering choice in tests (e.g., sort by id). Write a test file that covers: none, multiple mutuals, duplicate entries in friend lists, and empty lists. Constraints: len(currentFriends) up to 1e5 Example: A friends [2,3,4], B friends [3,4,5] => [3,4] Example Input A friends=[2,3,4], B friends=[3,4,5] Output [3,4]