Update Sources/Web3Core/Structure/Block/Block.swift

Co-authored-by: Jenea Vranceanu <36865532+JeneaVranceanu@users.noreply.github.com>

Author: h33min

Sources/Web3Core/Structure/Block/Block.swift

@@ -24,7 +24,9 @@ public struct Block {
     public var receiptsRoot: Data
     public var miner: EthereumAddress? // MARK: This is NOT optional in web3js
     public var difficulty: BigUInt
-    public var totalDifficulty: BigUInt? // MARK by JoshKim: Removed from Ethereum official Blockschema (https://github.com/ethereum/execution-apis/commit/9e16d5e76a554c733613a2db631130166e2d8725)
+    /// by JoshKim: Removed from Ethereum official Blockschema making it optional (https://github.com/ethereum/execution-apis/commit/9e16d5e76a554c733613a2db631130166e2d8725)
+    /// If decoding of this field has failed it will be set to 0 to avoid breaking changes. Will be made optional in v4 of web3swift.
+    public var totalDifficulty: BigUInt
     public var extraData: Data
     public var size: BigUInt
     public var gasLimit: BigUInt