How to use the harmonica.forward.utils.distance_spherical_core function in harmonica

def kernel_g_z_spherical(
    longitude, cosphi, sinphi, radius, longitude_p, cosphi_p, sinphi_p, radius_p
):
    """
    Kernel for downward component of gravitational gradient in spherical coords
    """
    distance, cospsi, _ = distance_spherical_core(
        longitude, cosphi, sinphi, radius, longitude_p, cosphi_p, sinphi_p, radius_p
    )
    delta_z = radius - radius_p * cospsi
    return delta_z / distance ** 3

def kernel_potential_spherical(
    longitude, cosphi, sinphi, radius, longitude_p, cosphi_p, sinphi_p, radius_p
):
    """
    Kernel function for potential gravitational field in spherical coordinates
    """
    distance, _, _ = distance_spherical_core(
        longitude, cosphi, sinphi, radius, longitude_p, cosphi_p, sinphi_p, radius_p
    )
    return 1 / distance