Added Arbitrum gas results handling feature

[kcharbo3]

What is this PR doing?

Adds a feature to retrieve and compute gas costs for Arbitrum whenever the measure-gas.ts script is run for the Arbitrum testnet. This script will send a BLS tx and a normal token transfer tx to the Arbitrum testnet. Then, the contracts/scripts/util/arbitrum-gas-util.ts file is called to pull in gas prices from Arbitrum mainnet and append the results to the contracts/ArbitrumGasCosts.md file.

Also updates the measure-gas script to run with the new version of the BLSExpander contract.

How can these changes be manually tested?

'npx hardhat run scripts/test/measure_gas.ts --network arbitrum_testnet'
command should succeed. After it runs, check the contracts/ArbitrumGasCosts.md file to see if two new rows have been added to the table.

Does this PR resolve or contribute to any issues?

No

Checklist

• I have manually tested these changes
• Post a link to the PR in the group chat

Guidelines

• If your PR is not ready, mark it as a draft
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[jacque006]

Nice work 👍 . Few nitpicks, but nothing that should hold this back.

Before we merge, could you please run the linter on the new/modified files.

# From project root
cd ./contracts
yarn lint --fix

Also @jzaki would be good to have you take a look as well.

[kcharbo3]

Ran the linter that made some changes. No errors for the new/modified files.