Problem when exporting OGS6 objects with elements of class numeric.

The export of OGS6 prj classes with numeric child objects (e.g. prj_jacobian_assembler$component_magnitudes) does not write these numeric vectors correctly into the corresponding PRJ file tag. As a result ogs6 can't read the input file correctly.

An example benchmark is Tests/Data/TH2M/THM/slab/THM_1d_dirichlet.prj.