`sim_cf_dens()` takes a list of power densities and returns simulated counterfactual densities.
sim_cf_dens(expected_number, base_dens, power_sim_results, window)
list of counterfactual densities, power as numerics, and expected number as a numeric
the expected number of observations
the baseline density (im object)
the results obtained by `simulate_power_density()`
owin object