Implement saving

[dmlary]

• [ ] Implement World::Helpers.save_player(player: entity, dest: path)
• [ ] Implement saving per-Entity
  • Convert Entity to hash containing difference from it's bases
  • Consider clearing all modified after base application if diff too slow
• [ ] Implement per-area saver
  • Use LoadedComponent to track output files

Need to be able to save by world, area, file, and single player.

[dmlary]

There's a concern here with save/load of player files and entity ids.

Currently when we create an entity, if no id is provided, we take the last base id, and add an incrementing digit to it. That entity id is unique for the run of the server, but NOT guaranteed to be unique across multiple runs. The problem is that the player saves, server reboots, we attempt to load the save, and entity id's collide.

Workarounds:

• At save time, generate UUID entity id's
• Prefix all loaded entities with a load-time unique prefix
  • How to we guarantee this is unique
• Make all entity id's UUIDs, and add a entity description field, and create a different mechanism to referencing entities in a human readable manner, or implement all the tooling required to never hand-write yaml again
• Capture DuplicateId, and generate a UUID entity id at collision time