Function calculate_hij

pub fn calculate_hij(
    phi_i: &[PolyVector],
    s: &[PolyVector],
    ep: &EnvironmentParameters,
) -> Vec<PolyVector>

calculate h_{ij} = 1/2 * (<\phi_i, s_j> + <\phi_j, s_i>), then use base b to decompose the polynomial

@param: phi_i: phi_i @param: s: witness s_i @param: ep: struct SizeParams

return h_{ij}