bug: SolvableOrders is filtering out orders by balance but not prioritising newer orders

[fleupold]

Problem

If a user places an order that doesn't get matched and then places a new order on top (without cancelling the old one), the second one may not make it into the auction because they may not have enough balance.

We used to evaluate the balance for orders sorted by order creation time (desc) to make sure we prioritise newer orders over older ones. I cannot find this logic anymore (in fact we filter out insufficient balance orders unsorted here)

Impact

Users may not get their replacement orders (or more recent limit orders) matched.

To reproduce

Place a small order with minimum slippage and a small amount (likely resulting in a negative objective value), which won't get matched. Then place another order with large slippage and see it also doesn't get matched until you cancel the first one. You'll also not see the order in the auction that the autopilot creates.

Expected behaviour

Second order is matched even without cancelling the first one.

Screenshots/logs

1. https://explorer.cow.fi/orders/0xe4ccfcb66df87901f7fa8ec1f54aba94df7f9ac836c4672e66df2eed0fb6b9b7c3792470cee7e0d42c2be8e9552bd651766c517865317b74 (eventually cancelled)
2. https://explorer.cow.fi/orders/0xba7f9ef98bc8742538f9310bb5662da2c16804bb1937d190c95930252cfd6347c3792470cee7e0d42c2be8e9552bd651766c517865317bf3 (not matched until ☝️ was cancelled)

[github-actions]

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