support deal on optimism sUSD

[sakulstra]

When i try to deal sUSD via deal(0x8c6f28f2F1A3C87F0f938b96d27520d9751ec8d9, user, 1 ether); on optimism foundry crashes with

[FAIL. Reason: stdStorage find(StdStorage): Packed slot. This would cause dangerous overwriting and currently isn't supported.]

Seems a bit similar, but probably different:

• deal does not work on Aave's aTokens or other tokens that perform computation in balanceOf #140

[adamxyzxyz]

Getting the same error when SNX, guessing this is a problem with any of their tokens. Any solution found for this?

[sakulstra]

For now we overwrite deal and for selected tokens, mock a whale and transfer instead of deal 😅

[ChiTimesChi]

@adamxyzxyz @sakulstra

Here's the solution we are using for minting sUSD in tests:

https://github.com/synapsecns/synapse-contracts/blob/4b2858a5f7aa3bed6c5c184ae1fe59c2730274ef/test/interfaces/ISynth.sol#L1-L13