 Here is the Python code based on your instructions, using the porepy library:

```python
import numpy as np
from porepy import *

def add_data_darcy(gb, tol, permeability, source, aperture, boundary_conditions):
    # Add Darcy's law parameters
    gb.add_data(DarcyLaw(permeability=permeability, source=source, aperture=aperture))
    gb.set_boundary_conditions(boundary_conditions)

def add_data_advection(gb, tol, source, porosity, discharge, boundary_conditions):
    # Add advection parameters
    gb.add_data(Advection(source=source, porosity=porosity, discharge=discharge))
    gb.set_boundary_conditions(boundary_conditions)
    gb.add_data(TimeStep(time_step=1.0))

tol = 1e-6
export_folder = "results"
time = 10.0
num_time_steps = int(time / 0.1)
time_step_size = 0.1
export_frequency = 1
coarsening = True

mesh_size = {1: 0.1, 2: 0.2, 3: 0.4}
domain_boundaries = {
    (0, 1): Line(Point(0, 0), Point(1, 0)),
    (1, 2): Line(Point(1, 0), Point(1, 1)),
    (2, 3): Line(Point(1, 1), Point(0, 1))
}

grid = Grid.from_csv("grid.csv")
grid.compute_geometry()
if coarsening:
    grid.coarsen()
grid.assign_node_ordering()

darcy_solver = DarcyAndTransport(grid, tol)
gb = grid.get_bucket()
add_data_darcy(gb, tol, permeability=1.0, source=0.0, aperture=1.0, boundary_conditions=DirichletBoundaryCondition(pressure=0.0))
solution, _ = darcy_solver.solve()
discharge, pressure = darcy_solver.extract_and_project_discharge_and_pressure()
total_flow_rate = np.sum(discharge)

darcy_solver.to_vtk(f"{export_folder}/darcy.vtk")

physics = AdvectionAndDiffusion()
advection_solver = LinearSystemSolver(grid, physics.advection_matrix, physics.advection_rhs)
mass_matrix_solver = LinearSystemSolver(grid, physics.mass_matrix, np.zeros(grid.num_nodes))

gb.add_data(advection_solver)
gb.add_data(mass_matrix_solver)
add_data_advection(gb, tol, source=discharge, porosity=1.0, discharge=1.0, boundary_conditions=DirichletBoundaryCondition(discharge=0.0))

A, b = physics.advection_matrix.to_matrix_and_rhs(grid)
L, P = advection_solver.factorize(A)
M = mass_matrix_solver.solve(grid.mass_matrix)

solution = np.zeros(grid.num_nodes)
production = np.zeros(num_time_steps)
time_steps = np.zeros(num_time_steps)

for t in range(num_time_steps):
    solution = advection_solver.solve(b)
    production[t] = np.sum(solution)
    time_steps[t] = t * time_step_size

    if t % export_frequency == 0:
        advection_solver.to_vtk(f"{export_folder}/advection_{t}.vtk")

advection_solver.to_pvd(f"{export_folder}/advection.pvd")
np.savetxt(f"{export_folder}/times.txt", time_steps)
np.savetxt(f"{export_folder}/production.txt", production)
```

This code assumes that you have a CSV file named "grid.csv" with the grid data. The grid data should be in the format:

```
node_id,x,y,z
0,0,0,0
1,1,0,0
2,1,1,0
3,0,1,0
...
```

The code also assumes that you have defined the `DarcyLaw`, `Advection`, `LinearSystemSolver`, `DirichletBoundaryCondition`, and other classes from the porepy library. If these classes are not defined, you will need to create them or adjust the code accordingly.