Integrate RPC client with contract calls #22

Description

Complete contract call integration with RPC.

Location

• File: src/contract/call.zig
• Lines: 130, 169

Current Status

Encoding works, execution not integrated.

Tasks

• Integrate eth_call
• Integrate eth_sendTransaction
• Build transactions from calls
• Gas estimation
• Result decoding
• Revert error handling
• Tests with mock RPC

Priority

Medium - For complete interaction