HyTeG coupling

Hi,

to me there seems to be an issue with the integration of hyteg_operators into hyteg. The hyteg_operators submodule in hyteg's current master [hyteg@a1fad041] stands at [4f3f7a53]. This commit is on branch thoennes/fix-cmake-dependencies, which has not been merged to main, yet.

Trying to build hyteg with main checked out in the submodule fails, because the list of includes passed to the compiler is incomplete. The following includes are missing:

-I[path-to-hyteg-dir]/src
-I[path-to-build-dir]/src
-I/usr/include/python3.11
-isystem [path-to-hyteg-dir]/walberla/src
-isystem [path-to-build-dir]/walberla/src

Merging thoennes/fix-cmake-dependencies locally into main resolved the issue for me. Thus, I guess the changes therein are essential.