OpenZeppelin contracts testing machine

[raulk]

I’d like us to focus on testing OpenZeppelin contracts: ERC20, ERC721, Governor, Upgradable contracts, proxies, etc. These would give us the most bang for the buck right now.

We should:

1. Bring all the OpenZeppelin smart contracts into the contracts directory.
2. Have test suites for hardhat, foundry, and brownie (in that order of priority) exercising deployment, transactions, calls, logs, etc. Try to re-use test suites that already exist.