fix: prefund num_wallets from base_mnemonic for non-persistent run

[mmsqe]

to avoid insufficient funds error when sender selection rotates when only prefund wallet[0] at genesis based on base_mnemonic

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Note

Medium Risk
Changes transaction funding and sender selection logic in the Ethereum loadtest runner, which can affect nonce usage and on-chain transfers during tests. Risk is moderate due to new prefunding transactions and altered sender rotation behavior, but scope is limited to loadtest execution.

Overview
Prevents finite (interval/block-bounded) Ethereum loadtests from failing when sender rotation reaches unfunded derived wallets by pre-funding zero-balance wallets from wallets[0] during NewRunner.

Updates load generation so contract deployments always use wallets[0] (without advancing the sender distribution), while all other messages use txFactory.GetNextSender() instead of random wallet selection; also defaults spec.InitialWallets to 1 when unset. Dependency bumps in go.mod/go.sum update bytedance/sonic and related indirect modules.

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