```python
import porepy as pp

def add_data(gb, domain):
    pass

def plot_over_line(gb, data_key, line_points):
    pass

tolerance = 1e-6
mesh_size_params = {"h": 0.1}
domain = {"xmin": 0, "xmax": 1, "ymin": 0, "ymax": 1, "zmin": 0, "zmax": 1}

gb = pp.GridBucket()
gb.create_grid("grid", gb.node_props(is_reservoir=True))
gb.compute_geometry()
gb.coarsen()
gb.assign_node_ordering()

add_data(gb, domain)

solver = pp.DualVEMMixDim(gb)
solver.assemble_matrix_rhs()
solver.solve()

solution = solver.split()
discharge, pressure = solution["discharge"], solution["pressure"]
projected_discharge = pp.project_discretization_matrix(gb, discharge)

pp.export_to_vtk(gb, "output.vtu", {"pressure": pressure, "discharge": discharge})

bounding_box = {"xmin": 0, "xmax": 1, "ymin": 0, "ymax": 1}
num_points = 10
x_points = pp.create_points_along_line(bounding_box, num_points, direction="x")
y_points = pp.create_points_along_line(bounding_box, num_points, direction="y")

plot_over_line(gb, "pressure", x_points)
plot_over_line(gb, "pressure", y_points)

print("Diameter of grid bucket:", gb.diameter())
print("Number of cells in 2D:", gb.num_cells(), "Number of cells in 1D:", gb.num_cells(1))
```