User Class Represents a user in the social network. Contains a Profile instance representing the user's details $($username$,$ password, screen name, email$).$ Manages user activities such as creating posts and sending messages.

Attributes:

profile $($Profile$)$: User's profile.

posts $($list of Post$)$: List of posts created by the user. messages $($list of Message$)$: List of messages sent by the user.

Methods:

$\_\_$init$\_\_($self$,$ username, password, screen$\_$name, email$)$: Initialize a User instance.

create$\_$post$($self$,$ content$)->$ Post: Create a new post for the user. Raise ValueError if the content of the post is empty.

send$\_$message$($self$,$ receiver, content$)->$ Message: Send a message to another user. Raise ValueError if the receiver ID or message content is empty.

$\_\_$str$\_\_($self$)$: Return a string representation of the User.