World merging - Allow a world (with/without physics) to merge into another world

[Bombfuse]

base_world.merge(another_world)

Imports all entities (without changing their id's preferably) and their physics bodies into the base world.

[Bombfuse]

This will also require guaranteeing that all entity's are spawned with a unique id, I'm unsure what work is required to do that right now