The auto restart logic was sending a USR2 to the parent process without checking what the parent process actually was. In some situations, it might not be the `bin/unicorn` supervisor.
This commit switches to use a global variable for the supervisor PID. This will be much less prone to unexpected behavior.
This commit adds a listener on (almost) all `.rb` files in the repository. When a change occurs, it checks whether Zeitwerk is responsible for autoloading it. If not, a warning will be printed to the console and the server will be automatically restarted. Optionally, you can pass the `AUTO_RESTART=0` environment variable to prevent auto-restart.