Add consensus-critical binary serialisation for blocks and transactions,
verified by computing the testnet genesis block hash and matching the C++
daemon output (cb9d5455...4963). Fixes Phase 0 type mismatches (variant
tags, field widths, missing fields) and adds encoder/decoder, tree hash,
and block/transaction hashing.
Key discovery: CryptoNote's get_object_hash(blobdata) prepends
varint(length) before hashing, so BlockHash = Keccak256(varint(len) || blob).
Co-Authored-By: Charon <charon@lethean.io>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
