Currently we're relying on the user's project setup to call find_package(..) and deal with the dependency headers themselves. This is poor form, arg_router's CMake package should do this.

I think it is just a case of adding target_link_libraries(arg_router PUBLIC Boost::boost) to library.cmake, but you'll have to look for changes in the generated arg_router.cmake to confirm. This isn't needed for span-lite as it is an optional dependency anyway.

• Update CMake package
• Update system package test to verify