Reintroduce `n_c_and_cpp` example

[joewallwork]

There was an unfinished C and C++ example in FTorch for some time. The draft code can be found in #230, which removed this example.

          Not for this PR but I wonder if we should remove this demo from the `main` branch and open an issue that would finish it? It's neither complete nor tested so perhaps not suited in v1.0.

Originally posted by @jwallwork23 in https://github.com/Cambridge-ICCS/FTorch/pull/228#discussion_r1910340522