feat add random mask to groth16 commitment

[Tabaie]

This PR adds a random mask to the BSB22 commitments in order to make them hiding.

It is achieved simply by randomizing a new variable and adding it to the commitment.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

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

[Tabaie]

@ivokub TestNoCommitmentVariable is failing because no commitment is truly empty anymore. Is that a desired feature or can we just remove the test?

[ivokub]

@ivokub TestNoCommitmentVariable is failing because no commitment is truly empty anymore. Is that a desired feature or can we just remove the test?

I made the test to expect provers success instead. It can be useful in the future to catch regressions. I think it is useful that we can have prover assigned random commitment if we don't commit to anything.

[ivokub]

I think it makes all sense! I added a regression test also.