[PoC] Working support for transfers (don't merge!)

[fedgiac]

Description

Just a draft PR with all experimental changes to make same-token orders work, built with the valuable help of @harisang and @fhenneke.

A local forked-node setup on mainnet with the baseline solver:

• Returns quotes for same-token orders with reasonable fee.
• Allows creating orders with same buy and sell token.
• Fills orders if the specified fee amount is that returned by the quote. The filled fee is consistent with the current gas price.

Note that the code is very horrible and any change is just there to make things work.
There are many things that should be carefully considered in an actual PR for this feature, notably PriceEstimating::estimate should probably split into two functions based on the purpose of the price estimation.

[github-actions]

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