[WIP] Cython language

[LecrisUT]

So I am playing around with creating a Cython language to try and simplify the way to make Cython files. The basic files that need to be created are documented here and I am looking at other implemented Fortran, CSharp, etc. languages for reference.

The end-goal is to make the CMakeLists.txt as:

cmake_minimum_required(VERSION 3.25...3.29)
project(simple LANGUAGES C Cython)

python_add_library(simple MODULE WITH_SOABI)
target_sources(simple PRIVATE simple.pyx)

install(TARGETS simple DESTINATION .)

Approach 1: set(CMAKE_Cython_OUTPUT_EXTENSION ".c")

The hope here is that we could define only the bare minimum to create the necessary .c files and have the C compiler part take over from there. Unfortunately CMake does not seem to chain the parts accordingly.

Maybe if we can manipulate the dependencies in .dep this approach would work.

Approach 2: chain CMAKE_Cython_COMPILE_OBJECT with CMAKE_C_COMPILE_OBJECT

This should probably work with the current implementation, and at first glance it seems to do what it needs to do, but the link-library part doesn't seem to be configured correctly yet

[LecrisUT]

With a6ad971 it somewhat works:

• Figure out why it appends .so twice. If you manually edit that, the installed files seem to import correctly
• Dependencies how?
• Could python_add_library also be simplified to add_library?