fix: fix OR computation in case one input is constant and other variable

[ivokub]

Description

See the added regression tests. If we had

api.Or(x, 1)

then the result was incorrectly computed for both x=0 and x=1. This was because we used a*(1-b) for computation not a+b-ab for OR. Furthermore, if we know that one input is constant then we do not have to add constraints as the result is always constant 1 if constant input is 1 and x if constant input is 0.

Reported by @wuestholz using gnark fuzzer. Thanks!

Type of change

• Bug fix (non-breaking change which fixes an issue)

How has this been tested?

• TestRegressionOr

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I did not modify files generated from templates
• golangci-lint does not output errors locally
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[gbotrel]

lgtm