bitcoin-spv - unnecessary type correction
The type correction `encodePacked().toBytes32()` is not needed as `sha256` already returns `bytes32`.\\n```\\nfunction hash256(bytes memory \\_b) internal pure returns (bytes32) {\\n    return abi.encodePacked(sha256(abi.encodePacked(sha256(\\_b)))).toBytes32();\\n}\\n```\\n
Refactor to `return sha256(abi.encodePacked(sha256(_b)));` to save gas.
```\\nfunction hash256(bytes memory \\_b) internal pure returns (bytes32) {\\n    return abi.encodePacked(sha256(abi.encodePacked(sha256(\\_b)))).toBytes32();\\n}\\n```\\n