unittest/python : add visualizer bindings visitor test, add CMake util to create C++ Python modules for tests

[ManifoldFR]

• unittest/python/CMakeLists.txt : add util function to create test C++ extension Python modules, and associated Python tests
• unittest/python : add test for visualizer bindings (visitor)

[github-actions]

👋 Hi,
This is a reminder message to assign an extra build label to this Pull Request if needed.
By default, this PR will be build with minimal build options (URDF support and Python bindings)
The possible extra labels are:

• build_collision (build Pinocchio with coal support)
• build_casadi (build Pinocchio with CasADi support)
• build_autodiff (build Pinocchio with CppAD support)
• build_codegen (build Pinocchio with CppADCodeGen support)
• build_extra (build Pinocchio with extra algorithms)
• build_mpfr (build Pinocchio with Boost.Multiprecision support)
• build_sdf (build Pinocchio with SDF parser)
• build_accelerate (build Pinocchio with APPLE Accelerate framework support)
• build_all (build Pinocchio with ALL the options stated above)

Thanks.
The Pinocchio development team.

[ManifoldFR]

@jorisv suggested 86547fb could fix the windows problem.

edit nope, didn't fix it :(

[ManifoldFR]

Following discussion with @jorisv, we've decided to temporarily not run the test on Windows until we have normalized paths for the binaries (like what he did for eigenpy).

[ManifoldFR]

@jcarpent this should be ready to merge.