Proof of Work Token

[ltardivo]

Enables client-side PoW minting for tokens on UTXO-based chains (Bitcoin, Litecoin, Dogecoin, Pepecoin) inspired from Bitcoin's architecture. Key features include dynamic difficulty adjustment, heaviest-chain consensus for fork resolution, and fungible token operations (transfer, merge, burn).

Key Changes

• Smart Contract Core (src/pow.ts): Added Pow class extending Contract for token minting with PoW validation.
• Integrated pure-JS Sha256 class (bit-identical to OpenSSL/Node.js crypto) for on-chain hash verification.
• Added isValid() for post-transfer validation via root revision sync.
• Miner Implementation (src/miner.ts): Created PowTokenMiner class for client-side mining loop (native crypto for speed).
• Heaviest-chain rule (cumulative work via 2^diff, tie-break by length).
• Configurable compute difficulty (e.g., intervals like 2016 for BTC/LTC, 1440 for DOGE).