Improve regression checking on tutorials

[andrsd]

Currently we only check that the input files run correctly, but we are not checking if they actually produce expected answers.

The table below summarizes if tutorials produce some output that can be used to check that they keep producing the expected answer or not

name	checks
aquad/product_GLC.py	✅ prints n_octants and n_dir_per_oct
aquad/sLDFE.py	outputs data into a file -> then displays a plot
lbs/keigen/pincell_example.py	✅ prints eigen_value
lbs/primer/forward_example.py	✅ prints ratio
lbs/primer/adjoint_example.py	✅ prints forward_total_flux,response
lbs/src_driven/detector_adj.py	✅ prints adjoint_total_response
lbs/src_driven/detector.py	✅ prints forward_total_flux,response
lbs/src_driven/glovebox_adj.py	✅ prints total_response_detector
lbs/src_driven/glovebox.py	✅ print total flux and response
lbs/src_driven/hdpe_example.py	produces a plot
logvol	no ckecking
mesh/mesh_extrude.py	exports pvtu file
mesh/mesh_ortho_2D.py	exports pvtu files
mesh/mesh_ortho_3D.py	exports pvtu file
mesh/mesh_read_obj_2D.py	exports pvtu file
mesh/mesh_read_gmsh_2D.py	exports pvtu file
mesh/mesh_read_gmsh_3D.py	exports pvtu file
mesh/mesh_read_vtu_3D.py	exports pvtu file
mesh/mesh_ortho_3D_blockIDs.py	exports pvtu file
xs/1g_xs_read_file.py	✅ prints several things
xs/mg_xs_read_file.py	✅ prints several things
xs/mg_xs_read_openmc.py	✅ prints several things
xs/1g_xs_simple.py	✅ prints several things

Mostly the mesh tutorials just produce a mesh file. Maybe, we could print number of nodes/cells for those?
The checkmarks indicate that there is something in the tutorial that could be used by the testing system to make sure the expect anser is produced by the code.

[ragusa]

1. aquad/sLDFE.py: maybe print out the number of directions and check that value or, better, printout one direction vector and check those 3 values
2. meshes: yes, maybe compare the number of cells
3. hdpe example: maybe compute the domain average and print that out
4. logvol: maybe use volumes_per_block = grid.ComputeVolumePerBlockID() and print out the volume of a block