The tests are missing negative tests and test-vectors

[cgrigis]

Security Code Review observation:

For example, it seems the shuffle tests are not testing the verification of a wrong shuffle nor providing test-vectors.

[K1li4nL]

At least the following packages are missing negatives:

• [x] shuffle
• [ ] proof/deniable
• [ ] proof/proof
• [ ] proof/dleq/dleq
• [ ] sign/anon (has no test)
• [ ] sign/bdn
• [ ] sign/cosi
• [ ] sign/schnorr
• [ ] sign/tbls