Refactoring idea: reuse `order_asset` and `price_asset` from the `Orderbook` instance

[serejke]

Overview

order_asset and price_asset are passed around into many parameters in code.

It may be possible to reuse fields of the Orderbook instance:

orderbook-rs/src/engine/orderbook.rs

Line 72 in 3210aa9

order_asset: Asset,

orderbook-rs/src/engine/orderbook.rs

Line 73 in 3210aa9

price_asset: Asset,