fix: fold boolean OR complements to true

[NullWitnessZK]

Fixes #247.

Minimal reproducer

Save as main.pl:

main(A: private bool, R: public u8) :-
    !A;
    A;
    R = 0x05.

The three cases form (!A) OR A OR (R == 5). Because !A OR A is always true, source semantics accept every R, including R = 6.

Compile through the normal Datalog proof pipeline at 271f911 and evaluate with R = 6:

raw source relation:       accepts R = 6
optimized IR:              (= R #x05)
pre/post R1CS and artifact: reject R = 6; accept R = 5

Expected

The entire disjunction folds to true.

Actual

The complementary pair is deleted, leaving only R == 5. A source-valid public input is rejected.

Why it happens

The wide BoolNaryOp::Or constant folder removes x and !x from its child set instead of returning true. Frontends can reach this n-ary form because Opt::Flatten runs before the final constant-fold pass.

Impact: overconstraint/completeness only.

Proposed fix

fix/cfold-or-complement at 65a9c14 returns true immediately when either ordering of a complementary pair is found.

The branch contains a self-contained regression:

cargo test b_or_complement

It checks both or(x, !x) and or(!x, x).