pub fn mzi_transfer_matrix(phase_rad: f64) -> [f64; 8]
MZI 2×2 transfer matrix elements (complex).
M = [[cos(φ/2), i·sin(φ/2)], [i·sin(φ/2), cos(φ/2)]]
Returns (re_00, im_00, re_01, im_01, re_10, im_10, re_11, im_11)