build: core library and each system separated to dedicated CMake targets

Refers to #249

example/alternative_namespaces/CMakeLists.txt

@@ -27,8 +27,8 @@ function(add_example target)
     target_link_libraries(${target}_alt PRIVATE mp-units::mp-units)
 endfunction()
 
-add_example(box_example)
-add_example(capacitor_time_curve)
-add_example(clcpp_response)
-add_example(conversion_factor)
-add_example(timer)
+add_example(box_example mp-units::si)
+add_example(capacitor_time_curve mp-units::si)
+add_example(clcpp_response mp-units::si)
+add_example(conversion_factor mp-units::si)
+add_example(timer mp-units::si)