Enhance Cython integration: Add support for c++ mode, use hostpython3-provided Cython, allow pinning of specific Cython version in recipe

[misl6]

Even if the target is switching to almost-fully-isolated builds for each recipe and take advantage of the additions made to Python3.13, this PR enhances our Cython integration with some features required for kivy/kivy development (current master branch requires c++ support on Cython files).

This PR also solves incompatibility issues related to cython-generated files when the Python version used to invokate the toolchain is different from the target one, by using the self-built hostpython3.

This PR does the following:

• Removed Cython from installation requirements, any "cythonization" will be performed by hostpython3.
• The appropriate Cython version will be installed by hostpython3 when required, as is now included into hostpython_prerequisites.
• The required Cython version can now be set via hostpython_prerequisites, this way every recipe can target its own specific Cython version.
• Support for recognizing, cythonizing and building/linking c++ files produced by Cython has been added.
• By default, Cython version used by CythonRecipe is 3.0.11. All recipes that are likely incompatible with Cython 3.x.x has been set to use Cython 0.29.37

⚠️ As all the CythonRecipe based-recipes have been touched, and some of these recipes are likely old and unmaintained, a failure during the CI/CD run is expected to happen.

[AndreMiras]

This is huge, I didn't know we could, thanks