Executed amounts - sanity checks

[josojo]

Currently, the executed amount of an order is not sanity checked.

We just the parsed order.execution_amount from the order

fn add_to_settlement(&self, settlement: &mut Settlement) -> Result<()> {
        use Execution::*;

        match self {
            LimitOrder(order) => settlement.with_liquidity(&order.order, order.executed_amount()),
}

and then based on it calculate the fee amounts:

fn compute_fee_execution(&self, fee_amount: U256) -> Option<U256> {
        match self.order.creation.kind {
            model::order::OrderKind::Buy => fee_amount
                .checked_mul(self.executed_amount)?
                .checked_div(self.order.creation.buy_amount),
            model::order::OrderKind::Sell => fee_amount
                .checked_mul(self.executed_amount)?
                .checked_div(self.order.creation.sell_amount),
        }
    }

I think we should make sure that the for a partially fillable order the "executed amount <= sell amount" and for a killorfill order "executed amount== sell_amount".
Felix noticed that issue due to a bug in the cow-dex-solver, it's providing too big executed amounts, and then we run into this issue. I will try to fix the bug on the cow-dex solver side.