sBTC / Nakamoto: Contract Interfaces for Allowing the Node to Maintain sBTC

[jcnelson]

The Stacks node will call into sBTC to carry out various maintenance duties. For example (this is incomplete):

• Processing consolidations to mint sBTC
• Processing withdraw transactions on BTC to burn sBTC
• Processing and clearing deposit challenges
• Validating and clearing proof-of-withdraw BTC transactions posted by Stackers (so PoX can keep going even if the tx does not get mined)
• Activating/deactivating PoX payouts based on sBTC liveness

I think there are others

[AshtonStephens]

Needs list of things a stacks node needs to assist sBTC. We need a strict list of requirements.

Will likely determine next week in calls with @saralab @kantai @jcnelson, @soju-drinker, @jferrant etc.

A number of these questions will be addressed in contract interactions design document that we'll post here.

[AshtonStephens]

Need to isolate the end to end flows of the sBTC operations. Then we can sign off on the design document.