Smart contract fixes: address validation, balance key prefix, config + script cleanup

[Bismanpal-Singh]

Summary

• GlobalState balance keying: Use contract_balance_<address> for GetBalance/SetBalance to avoid key collisions.
• Input validation: Add strict EVM-style address checks (0x + 40 hex chars) to tool commands:
  • init owner address
  • execute caller and contract addresses
  • get_balance/set_balance addresses
• New server config: Add service/tools/config/server/contract_server.config with local 4-node setup, LevelDB tuning, and consensus flags.
• Script cleanup: Remove merge markers from start_contract_service.sh; retain license header and ensure clean startup.