src: use callback scope for main script

This allows removing custom code for setting the current async ids
and running nextTicks.

PR-URL: https://github.com/nodejs/node/pull/30236


Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>