[Zig] Implement Transaction builder utilities

[roninjin10]

Summary

Implement Transaction builder utilities in Zig to match TypeScript.

Required Features

Transaction Types

• Legacy (type 0)
• EIP-2930 Access List (type 1)
• EIP-1559 (type 2)
• EIP-4844 Blob (type 3)
• EIP-7702 (type 4)

Builder Pattern

• TransactionBuilder struct
• Fluent API for setting fields
• Automatic type detection
• Gas estimation integration

Utilities

• serializeTransaction - RLP encode for signing
• parseTransaction - Decode raw transaction
• getTransactionHash - Calculate tx hash
• recoverSender - Recover from address

Signing Integration

• signTransaction - Sign with private key
• serializeSignedTransaction - Encode signed tx

Current State

Basic transaction types exist but no builder utilities.

Note: Issue created by Claude AI assistant, not @roninjin10 or @fucory