implement a fix for CO15

[themighty1]

The base OT protocol CO15 used in mpz is known to have a broken security proof. In this discussion https://github.com/emp-toolkit/emp-ot/issues/74 it was suggested to use a fix from https://eprint.iacr.org/2018/499 But that fix (see APPENDIX A) introduces a selective failure attack.

We need to investigate if the selective failure attack is acceptable within the context of the TLSNotary protocol. If it is acceptable, we need to implement the fix.

[themighty1]

This paper https://eprint.iacr.org/2025/493 gives a UC proof for CO15 but requires some modifications to the original CO15 protocol.