support arc testnet

[koo-virtuals]

Note

Medium Risk
Moderate risk because it updates deployment/verification network configuration and automated deploy scripts, which could affect where contracts get deployed and with what defaults. Functional contract code is unchanged, but misconfiguration could lead to incorrect network targeting or liquidity parameters.

Overview
Adds Arc Network support across tooling: updates hardhat.config.js with arc_testnet/arc_mainnet RPC + Blockscout (Etherscan-compatible) explorer settings, and extends run_local_deploy.sh to accept these networks (including a mainnet safety prompt) and to run the UniV2 liquidity helper on arc_testnet.

Also tweaks the UniV2 testnet liquidity script default LIQUIDITY_AMOUNT from 10 to 1, and commits a new OpenZeppelin upgrades manifest .openzeppelin/unknown-5042002.json for chainId 5042002 (Arc testnet).

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