rive-unity libraries not producable from rive-cpp

I am looking to expand on the capabilities provided by the rive-unity package, however the binaries which are provided in the rive-unity package are not producible from the rive-cpp repo, as the native bindings present in the rive-unity package do not exist in built libraries.

An example of one of the native bindings would be:

rive-unity/package/Runtime/SMIInput.cs at f76a495e59ce19dca0cae1216108968c6cb2d2a4 · rive-app/rive-unity (github.com)

Right now it is impossible to change or make contributions to expand upon simple functionality such as exposing values. The rive-unity github is also unfortunately not at all managed with issue count growing.

Can we please have instructions, if my assessment is correct, on how to produce the binaries so functionality can be expanded for rive-unity