Cmake build system

[greole]

This PR adds some basic cmake setup, this includes

• application and src can be compiled together or separately see -DNEOFOAM_BUILD_APPS
• a basic Gtest setup which pulls Gtest from a remote
• some compiler, sanitizer, etc options based on https://github.com/cpp-best-practices/cmake_template/tree/main
• a cmake-format target (needs cmake-format to be installed)

In a separate PR we should handle

• a file formating target
• better defaults for installation paths ($FOAM_USER_LIBBIN?)

[HenningScheufler]

Regarding the modules are the compatible with the current release of OpenFOAM or the require significant modification inside the OpenFOAM legacy?

[greole]

Regarding the modules are the compatible with the current release of OpenFOAM or the require significant modification inside the OpenFOAM legacy?

That depends on how exactly we implement NeoFOAM. If we just emit a libOpenFOAM.so and libFiniteVolume.so to overwrite the existing one than modules don't interfere. However, this might be impractical since we need to match OpenFOAMs the ABI to avoid having missing symbol errors at runtime. A safer option would be to step by step migrate the applications. Ideally migrating just means copying the solver folder to applications and to replace the #include fvCFD by import NeoFOAM