Stop making core landmass code generic. #167
Description
Currently, landmass always includes the generic argument in Archipelago, Island, Agent, Character, etc. This means we can't codegen these until they get monomorphized. This also leads to annoying things like markers everywhere, having to convert points to landmass multiple times, etc.
If we split this into a "core" set with no generic, and then provide a generic interface on top, that would be ideal! Most of our code can compile without waiting on generics, with only the input/output having to wait for the generic args to monomorphize. This would also allow bevy_landmass to only depend on the core with no generic, allowing more direct access, and I think tighter integration with the ECS.
This would also help #31, since our systems can be non-generic, and then we only need lightweight systems to convert the positions to/from landmass.
It could also slightly help with performance since we can do these coordinate conversions once up front.