Add GCC 12-14 as well as Clang 16-18 to CI/CD and fix warnings

[auto-differentiation-dev]

Currently, the CI/CD workflows test GCC versions 5-11. The latest version however is GCC 14. To ensure support for these new compiler releases, we should add them to the CI/CD pipeline. The same goes for the newer versions of Clang mentioned in the title.

Further, from local compilations, it looks like GCC 12 onwards triggers a few warnings with the XAD code. These warnings should be carefully assessed and fixed (not suppressed).

We could use a container like this one to build for GCC version 7 to 14 onwards and this one for Clang 11-18.

We can probably drop support for GCC 5 and 6 at that point, as they are very old. This would allow us to remove the older containers that are used for builds at the moment, which have issues supporting newer versions of the GitHub actions.