Design and implement a simplified version of a social media platform's feed system. The system

should support the following functionalities:

$1.$ Users can post new messages to their feed.

$2.$ Users can follow other users.

$3.$ Users can view their own feed, which consists of messages from users they follow, sorted

by the timestamp of the messages.

$4.$ Users can unfollow other users.

$5.$ Users can view the feed of a specific user they follow