Design and implement a full-fledged undo-redo system

[alice-i-cecile]

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[10:34 PM]Alice 🌹: I think that there's a lot of interesting and important complexity to tackle with undoing, and I really like the contextual / nested undo-redo + a trait based approach [10:34 PM]Alice 🌹: But for now, a relatively simple trait will do [10:36 PM]Alice 🌹: I'd also like to lean away from a snapshot-based approach if possible, and avoid a distinct storage (sorry @nth but I've worked with this and I found it very frustrating) [10:36 PM]Alice 🌹: There's definitely a chance that we can't make that sort of design work, but I'm happy to cross that bridge when we get there

This is a followup to #2, which is a simple design to get us started.

Cross-posted from Discord.