Fix the sign of res1

[weikengchen]

During the calculation of the constraint numerator, the sign for res1 is indeed wrong. This was not caught before because the res1 polynomial was "linear" in the case of the Fibonacci example and therefore would be simply zero everywhere.

This was caught during the implementation of the recursive verifier.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files with missing lines	Coverage Δ
...dsl/plonk/part2_fiat_shamir2_and_constraint_num.rs	93.10% <ø> (ø)