feat: allow optional order book override for market price

[melonges]

Note

Low Risk
Low risk, small additive API change confined to calculateMarketPrice; main concern is downstream callers passing stale/incorrect OrderBookSummary, affecting quoted prices.

Overview
ClobClient.calculateMarketPrice now accepts an optional orderBook override and uses it when provided instead of always fetching via getOrderBook.

This enables callers to reuse an already-fetched OrderBookSummary to avoid extra network requests while keeping existing behavior as the default.

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