EIP-7702 SetCode transaction support (type 0x04)

[koko1123]

Motivation

EIP-7702 (Pectra) is live on mainnet; alloy and viem both ship it. transaction.zig covers legacy/2930/1559/4844 but cannot sign or serialize type-0x04 transactions — a parity gap that ages the library.

Scope

• authorization_list type: {chain_id, address, nonce, y_parity, r, s} with its own signing hash (keccak256(0x05 || rlp([chain_id, address, nonce])))
• Type 0x04 serialization for signing and broadcast in transaction.zig
• Signer.signAuthorization helper
• RPC parse: authorizationList in rpc_transaction.zig

Pointers

Follow the EIP-4844 plumbing in transaction.zig end-to-end. Spec: https://eips.ethereum.org/EIPS/eip-7702