blockmesh files tgv and cbox produced with blockmeshhelper

Currently, the blockMeshDict files in these solvers are produced with a jinja template. Let's try to produce them with blockmeshhelper.

See:

• https://foss.heptapod.net/fluiddyn/fluidsimfoam/-/blob/branch/default/doc/examples/fluidsimfoam-tgv/src/fluidsimfoam_tgv/templates/blockMeshDict.jinja
• https://foss.heptapod.net/fluiddyn/fluidsimfoam/-/blob/branch/default/doc/examples/fluidsimfoam-cbox/src/fluidsimfoam_cbox/templates/blockMeshDict.jinja