Optimized zk randomization

[UlrichHaboeck75]

Due to changing our previous multi-point multi-poly open to the real protocol from Boneh, Gabizon et al. (see polycommit, issue 19) , we are now able to randomize the witness-related polynomials w(X), y_A(X), y_B(X) as well as the outer sumcheck boundary U(X) (called Z(X) in the code) using zero-knowledge bound b=0 (instead of b=1).
That means,

• the former three polynomials are randomized using constant multiples (instead of linear polynomials) c_0 * v_H(X) of the vanishing polynomial v_H(X), and
• the boundary U(X) is randomized by linear, i.e. (c_0+c_1*X) multiples of v_H(X).