Feat: use block proposal struct for miner -> signers communication

[kantai]

This uses a struct for communicating a block proposal from the miner to signers.

The signer also checks the claimed reward cycle of the block before attempting to validate the proposal.

[obycode]

LGTM!

[codecov]

Codecov Report

Attention: Patch coverage is 81.25000% with 12 lines in your changes are missing coverage. Please review.

❗ No coverage uploaded for pull request base (dream-team-fixes@db8f0cc). Click here to learn what that means.

Additional details and impacted files

@@                 Coverage Diff                 @@
##             dream-team-fixes    #4511   +/-   ##
===================================================
  Coverage                    ?   70.47%           
===================================================
  Files                       ?      452           
  Lines                       ?   326113           
  Branches                    ?      323           
===================================================
  Hits                        ?   229824           
  Misses                      ?    96281           
  Partials                    ?        8           

Files	Coverage Δ
stackslib/src/chainstate/nakamoto/miner.rs	76.09% <100.00%> (ø)
libsigner/src/events.rs	79.42% <94.73%> (ø)
testnet/stacks-node/src/nakamoto_node/miner.rs	79.27% <81.48%> (ø)
stacks-signer/src/signer.rs	70.52% <62.50%> (ø)

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