feat: amm market depth perf - only calculate levels if they change an…

[wwestgarth]

This should help the datanode performance on the AMM auction uncrossing tests in the overnight system-tests runs. Changes are:

• expansion price levels for market-depth are only calculated up to the widest AMM (previously we'd expand fully based on the config parameters, then later ignore levels)
• we cache the calculation levels since if the mid-price doesn't change, nor does the expansion levels so we can just pull out ones we already have