Implement Identifiable Aborts (take 2)

[real-or-random]

Implement the idea from https://github.com/BlockstreamResearch/bip-frost-dkg/issues/9#issuecomment-2220091151, ideally in a PR so we can judge the complexity.

Steps:

• [ ] Coordinator should probably check the messages received as far as possible (https://github.com/BlockstreamResearch/bip-frost-dkg/issues/29) and raise InvalidContributionExcpetion
• [ ] The actual implementation of the idea
• [ ] Change BIP text to explain IA (this needs to say that the coordinator is fully trusted for IA)

[real-or-random]

One natural way to do this is to let each coordinator_step return additional blame data, separate for each participant. This could be an easy way of making IA optional: Just skip computing and sending this data around.

Not sure if it's worth making IA optional, but at least the additional complexity over non-optional IA is tiny.