Replace FIX-protocol-based integration tests with tests using real cTrader
types (ICMarketsConfig, TradingOrder, BrokerInterface). All 21 tests pass:
broker_failover (5), icmarkets_validation (10), order_lifecycle (6).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Add rate limiter (50/s + 5/s historical), symbol mapper, order builders,
account queries, market data subscriptions, and high-level CTraderClient
that orchestrates the full connect/auth/symbol-load lifecycle.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
