feat: migrate USDⓈ-M futures WS to /public /market /private endpoints

[pcriadoperez]

Route futures WebSocket streams to Binance's new category-based URLs (public/market/private) per the 2026-03-06 upgrade notice.
Auto-classifies streams: bookTicker/depth → /public/, aggTrade/kline/ticker/etc → /market/, listenKey → /private/.
Demo/test environments keep legacy URLs. Legacy production URLs retire 2026-04-23.

[pcriadoperez]

Test Results — 35 passing (11s)

New migration tests (30 tests):

  classifyFuturesStream
    ✔ classifies bookTicker as public
    ✔ classifies depth streams as public
    ✔ classifies aggTrade as market
    ✔ classifies markPrice as market
    ✔ classifies kline as market
    ✔ classifies ticker as market
    ✔ classifies miniTicker as market
    ✔ classifies forceOrder as market
    ✔ classifies compositeIndex as market
    ✔ classifies contractInfo as market
    ✔ classifies assetIndex as market
    ✔ classifies listenKey as private

  getFStreamSingleUrl with category
    ✔ returns public ws URL
    ✔ returns market ws URL
    ✔ returns private ws URL
    ✔ returns legacy URL without category

  getFStreamUrl with category
    ✔ returns public stream URL
    ✔ returns market stream URL
    ✔ returns private stream URL
    ✔ returns legacy URL without category

  Demo mode uses category-based URLs
    ✔ getFStreamSingleUrl returns demo URL with category
    ✔ getFStreamUrl returns demo URL with category
    ✔ getFStreamSingleUrl returns legacy demo URL without category
    ✔ getFStreamUrl returns legacy demo URL without category

  Private stream URL uses query params for listenKey
    ✔ constructs ?listenKey= URL instead of path-based
    ✔ constructs query-param URL for demo too

  Live: production market stream (aggTrade via /market/)
    ✔ receives aggTrade data from /market/ endpoint

  Live: production public stream (bookTicker via /public/)
    ✔ receives bookTicker data from /public/ endpoint

  Live: demo private stream (userFutureData via /private/)
    ✔ connects to private user data stream successfully

  Live: production combined market stream (kline via /market/)
    ✔ receives kline data from /market/ combined stream

Existing futures WS tests (5 tests, regression check):

  Websockets candlesticks
    ✔ Calls spot candlesticks websocket
  Websockets futures ticker stream
    ✔ Calls prevDay websocket for symbol
  Websockets miniticker
    ✔ check miniticker websocket
  Websockets chart
    ✔ Calls chart websocket
  Websockets aggregated trades
    ✔ Calls trades websocket

Live tests verified against:

• Production /public/ws/, /market/ws/, /market/stream?streams=
• Demo /private/ws?listenKey= (userFutureData)