Verify quote with pre interactions

[MartinquaXD]

Description

Not too long ago #3081 changed the simulation logic to not do any set up steps on behalf of the user if the quote provided some pre-interactions. That was done to avoid reverts when a pre-interactions actually set up everything for the trade (e.g. get balances by unstaking).
However, this caused issues with verifying quotes with permit pre-interactions. Because the quote provided the permit pre-interaction the simulation logic also did not try to fake balances although it could have.

Changes

Now we again always call the code to setup approvals and such BUT we do it as the very last pre-interaction. That way this operation becomes a no-op if the user already sets up everything with their pre-interactions OR does the usual logic and reverts with helpful error messages if the pre-conditions can't be met.
Since this function may now be a no-op I renamed it to ensureSwapPreconditions().
Additionally this moves code that was previously run before the settlement inside the settlement which increases the measured gas cost. To work around that I also introduced a wrapper function in Solver.sol that simply calls the Trader function and discounts the gas costs. Note that we can't simply do the necessary steps in the Solver because we need to be inside the context of the Trader to be able to set approvals and such.

That way we can verify quotes which do no, partial or the entire swap setup in their pre-interactions while keeping good error messages and accurate gas estimates.
Kudos to @nlordell for the idea.

How to test

I added an e2e test that fails without the PR.

[nlordell]

However, this caused issues with verifying quotes with permit pre-interactions. Because the quote provided the permit pre-interaction the simulation logic also did not try to fake balances although it could have.

Does this mean that the user is signing a permit allowance without actually having balances? Feels weird to request a quote with a legitimate allowance signature if you don't intend to trade.

[MartinquaXD]

Does this mean that the user is signing a permit allowance without actually having balances? Feels weird to request a quote with a legitimate allowance signature if you don't intend to trade.

Yeah, fair point. OTOH we started to support the use case where users can open orders for which they currently don't have the balance. Maybe that's an issue where @alfetopito could chime in but overall the proposed solution feels like the lesser of 2 evils.

[squadgazzz]

I spent more time than anticipated to find potential pitfalls or other workarounds, but actually couldn't come up with anything. The mentioned tradeoffs make sense.

[alfetopito]

Does this mean that the user is signing a permit allowance without actually having balances? Feels weird to request a quote with a legitimate allowance signature if you don't intend to trade.

Yeah, fair point. OTOH we started to support the use case where users can open orders for which they currently don't have the balance. Maybe that's an issue where @alfetopito could chime in but overall the proposed solution feels like the lesser of 2 evils.

if you don't intend to trade.
It's not that a user does not intend to trade or don't have the balance (well, they don't, that's true).
The goal is to allow the balance to be funded from a pre-hook and used in the order.
Quick example: Claim an airdrop/exit a pool then use whatever is coming as a sell token.

You can already do that in the UI by turning on the Hooks tab, currently hidden behind a setting:

[squadgazzz]

Cool, the updated version seems much better 🙌