7DRL days 1-2

This is intended to be a mech game for 7DRL. I didn't get as much done over the first two days as I was hoping, but basics of movement and the item model are working.

The plan is to have a time system which allows movement and weapons to be activated with separate turns. It remains to see if that is actually playable.

I am starting from an existing codebase that covers UI and some basics like saving and restoring games. It uses bracketlib for rendering, with Ratatui for UI (with a connecting package for that).