Draft: gcg-static-mesh: Enable static mesh caching in ghost cell generator filter

Add an option to the GhostCellGenerator filter to enable static mesh caching. With the option enabled, the first filter update will generate the ghost cells and cache the result. Subsequent calls will then only synchronize the point/cells arrays, eliminating the need to regenerate the ghost cells as long as the upstream geometry does not change. This is a draft for now, the feature will benefit from other developments in generalizing GetMeshMTime to other dataset types.