feat: add swap strategy

[royvardhan]

A swap strategy will the following rules:

1. canFill: Only checks whether the filler has enough balance to fill the order outputs. This comparison happens in USD value only, as we later swap tokens to derive the output tokens. If the filler wallet's USD value exceeds the order outputs, we can probably fill the order.
2. calculateProfitability: Checks what the filler will receive versus what the filler will spend with the following formula

const toReceive = outputUsdValue + order.fees // USD value
const toPay = inputUsdValue + totalGasCostUsd // USD value
const profit = toReceive - toPay

3. executeOrder: Fills the order by deriving the missing output tokens by swapping

[royvardhan]

I'm not including V4 because it requires unlock patterns with IUnlockCallback that regular wallets can't handle directly. EIP-7702 workaround can be used, as the BatchExecutor contract code we are inheriting right now as an EOA can be updated. But it will add complexity to the contract.

V2/V3 already provide good liquidity coverage with simpler integration, and V3 uses the same fee structure the V4 does.

[Wizdave97]

How does the callback affect swapping in the pool? Don't EOAs currently interact with UniV4?

[Wizdave97]

Ohh, I see what you mean here https://docs.uniswap.org/contracts/v4/reference/core/PoolManager#unlock

[royvardhan]

Yes correct. If we knew the amountIn already, we could easily send v4 swap to universal router as it handles everything.

To get the amountIn through the v4 quoter, we need to call quoteExactInputSingle which is a write function. This works through callback to the caller, always ending up reverting with revert reason being the amountIn, and gasEstimate data