Unified async Rust API for 47 exchange connectors (REST + WebSocket). The core layer — pure ExchangeHub + connectors. Higher-level builder, persistence, replay, OB tracker live in `digdigdig3-station`.
//! # L2 — L1 + orderbook data (no execution)
//!//! L2 connectors provide full market data including orderbook depth,
//! but do NOT support trading or account operations.
pubmodfree;pubmodpaid;