Nakamoto Signer[3.0] - The sign_coordinator must be updated to send a block proposal message rather than initiate a signing round

[saralab]

stacks-node: nakamoto_node::sign_coordinator

The sign_coordinator must be updated to send a block proposal message rather than initiate a signing round (with a NonceRequest). It will listen on the stackerdb for signer responses, as it does currently, but the signer responses will be MessageSignatures, rather than WSTS packets.

The sign_coordinator will need to validate the signatures and tally the results. Once the validation threshold is reached, they can announce the block.

[hstove]

NB: The function begin_sign_v0 was added in #4781 , and the work for this ticket can continue in that code:

stacks-core/testnet/stacks-node/src/nakamoto_node/sign_coordinator.rs

Line 656 in d14e5b4

// TODO: get messages from signers