Add the vulnerable code to the repository

[joaquinlpereyra]

When possible (ie: when the vulnerable code is verified, or we know its github, or we somehow have access to its sourcecode...) we should strive to add it to the repository, possibly to the test itself.

By itself, this would be a win, as it is easier to read: instead of going to etherscan and finding my way through their serviceable but not great code viewer, I can just inspect it here right next to the attack.

And with a bit of tinkering I think this would allow us to go even further and use Foundry's step-by-step debugger on attacks, which would be amazing to understand all the details of each exploit.