System library relative imports are broken for systems in a namespace

[Kooshaba]

sup bros

the problem i'm seeing comes from the fact that system interfaces are generated in the top-level codegen folder regardless of the namespace they are in, but system libraries are generated in namespace specific codegen folders. the same logic is used to generate relative imports in both situations, so the system library imports end up being wrong.

Branch showing failure using system lib tests: https://github.com/latticexyz/mud/tree/kooshaba/system-lib-imports

✌🏼