feat: set block beneficiary to proposer address

[qj0r9j0vc2]

Summary

• Set block header beneficiary to the proposer's Ethereum address for proper reward attribution
• Add ethereum_address field to ConsensusValidator loaded from genesis
• Include proposer_id and proposer_address in Cut hash for tamper-proof attribution
• Thread beneficiary through ExecutionBridge and node execution flow

Test plan

• Unit tests for Cut hash with proposer fields
• Unit tests for CutAssembler preserving proposer info
• Borsh backward compatibility for ConsensusValidator
• cargo check passes
• cargo fmt passes