  Here is the Python code based on the instructions:
```
import porepy as pp
import numpy as np
import matplotlib.pyplot as plt

# Define two functions
def add_data(grid_bucket, domain):
    # Define permeability, apertures, and boundary conditions
    grid_bucket.permeability = np.ones(grid_bucket.shape)
    grid_bucket.apertures = np.zeros(grid_bucket.shape)
    grid_bucket.boundary_conditions = np.zeros(grid_bucket.shape)

def plot_over_line(grid_bucket, line, x_axis, y_axis):
    # Plot values over a line in a grid bucket
    x = np.linspace(line[0], line[1], 100)
    y = np.linspace(line[2], line[3], 100)
    z = np.zeros((100, 100))
    for i in range(100):
        for j in range(100):
            z[i, j] = grid_bucket.get_value(x[i], y[j], x_axis, y_axis)
    plt.pcolor(x, y, z)
    plt.colorbar()
    plt.show()

# Set tolerance value and mesh size parameters
tolerance = 1e-6
mesh_size = 10

# Import a grid bucket from a CSV file
grid_bucket = pp.GridBucket.from_csv("grid_bucket.csv")

# Compute geometry, coarsen, and assign node ordering
grid_bucket.compute_geometry()
grid_bucket.coarsen(mesh_size)
grid_bucket.assign_node_ordering()

# Use the add_data function to assign parameters to the grid bucket
add_data(grid_bucket, domain)

# Define a solver using the DualVEMMixDim class for flow
solver = pp.DualVEMMixDim(grid_bucket, domain)

# Compute the matrix and right-hand side of the system
A, b = solver.compute_system()

# Solve the system
x = np.linalg.solve(A, b)

# Split the solution, extract the discharge and pressure, and project the discharge
solver.split_solution(x)
discharge = solver.extract_discharge()
pressure = solver.extract_pressure()
projected_discharge = solver.project_discharge(discharge)

# Export the grid bucket to a VTK file, including the pressure and discharge
grid_bucket.export_to_vtk("grid_bucket.vtk", pressure, discharge)

# Define a bounding box and a number of points
bounding_box = pp.BoundingBox(0, 10, 0, 10)
num_points = 100

# Create two sets of points along the x and y axes
x_points = np.linspace(bounding_box.x_min, bounding_box.x_max, num_points)
y_points = np.linspace(bounding_box.y_min, bounding_box.y_max, num_points)

# Use the plot_over_line function to plot the pressure along these lines and save the results to CSV files
for i in range(num_points):
    for j in range(num_points):
        line = [x_points[i], x_points[i+1], y_points[j], y_points[j+1]]
        plot_over_line(grid_bucket, line, "x", "y")
        plt.savefig(f"pressure_along_line_{i}_{j}.png")
        plt.close()

# Print the diameter of the grid bucket and the number of cells in 2D and 1D
print(grid_bucket.diameter)
print(grid_bucket.num_cells_2d)
print(grid_bucket.num_cells_1d)
```