Implement Portals for the Factorio Subsystem.

Decide on an approach for which the Factorio subsystem will handle portals (this will require some discussion), and implement the code necessary to maintain the list of existing portals and their configurations, and somehow run code on them each tick.

Start by locating the Factorio subsystem and reviewing how it currently represents game state and tick processing. Discuss and decide how portals should be represented, configured, maintained, and executed each tick; completion requires implementing that agreed approach.

Written by the indexing model from the issue text.