Add compiler caching

By default, the best we can do is artifact builds between stages, which leads to unnecessary recompilation.

Is the introduction of Ccache as a CI dependency a suitable improvement to this?

This can be enabled by adding -DCMAKE_CXX_COMPILER_LAUNCHER=ccache. It supports cache size management, which will allow us to cache multiple relevant builds in the pipeline and ensure it does not exceed the artifact size limit. Note: Gitlab CI caching feature is not suitable for our default runner unless we set up a cache server.