feat: add reusable market helper APIs

[mtshit]

Summary

• add reusable MarketInfo and TradingPermissions helpers for market status, order capability, quote precision, notional limits, and effective lot constraints
• add reusable Kline collection helpers for dedup/merge/window operations
• keep MarketData focused on atomic fetch operations by requiring market(&Symbol) and moving map/history assembly into MarketDataExt
• implement Binance single-symbol market lookup with exchangeInfo(symbol=...) instead of routing through a full-market fetch

Notes

• #[async_trait] stays in place intentionally because ExchangeHandle stores Arc<dyn MarketData> and the current handle model relies on object-safe async traits
• last_prices(Option<&[Symbol]>) and the shared mkt_core::Error surface are unchanged in this round; the follow-up focuses on the concrete performance and trait-boundary issues

Commit Breakdown

• 8d6b750 Add market helper methods
• b97fcb3 Add kline collection helpers
• ba0ef99 Fold market data helpers into MarketData
• 4dd6f6b Split market data helpers from core trait

Tests

• cargo test -p mkt-types -p mkt-core