Fast Finalization

The sub-second transaction finality goal of the Alpenglow consensus protocol, targeting approximately 150 milliseconds from block production to irreversible confirmation. Fast finalization is achieved by replacing Tower BFT's exponential lockout mechanism (which requires ~31 confirmations over ~12.8 seconds) with Alpenglow's certificate-based approach where a single round of supermajority voting produces an irrevocable finality proof.