FeedClient missing `watchOrderBook` in both SDKs despite core `IDataFeed` declaring it

[realfishsam]

Gap

The core IDataFeed interface declares watchOrderBook?(symbol, callback) and lists 'watchOrderBook' as a DataFeedCapability. Neither the TypeScript nor the Python FeedClient exposes this method.

Current state

Core (core/src/feeds/interfaces.ts:14, 37):

// DataFeedCapability union includes:
'watchOrderBook'

// IDataFeed interface declares:
watchOrderBook?(symbol: string, callback: (book: OrderBook) => void): () => void;

TypeScript SDK (sdks/typescript/pmxt/feed-client.ts): methods present — listFeeds, loadMarkets, fetchTicker, fetchTickers, fetchOHLCV, fetchOracleRound, fetchOracleHistory, fetchHistoricalPrices. No watchOrderBook.

Python SDK (sdks/python/pmxt/feed_client.py): same set of methods. No watch_order_book.

Related issues:

• FeedClient missing fetchOrderBook in both SDKs despite the sidecar exposing the route #191 — fetchOrderBook missing from FeedClient (static snapshot, different method)
• watchTicker() on data feeds (BinanceFeed, ChainlinkFeed) is in core but not accessible through either SDK or the server #506 — watchTicker missing from FeedClient (streaming ticker, different method)
• FeedClient missing fetchFundingRate and fetchFundingRates in both SDKs #932 — fetchFundingRate/fetchFundingRates missing

Expected behaviour

Both FeedClient implementations should expose watchOrderBook(symbol, callback) / watch_order_book(symbol, callback) that streams live order book updates from the feed sidecar endpoint (e.g. /api/feeds/{feed}/watchOrderBook).

Impact

Real-time order book data from data feeds (Binance, etc.) is inaccessible through either SDK.