Add FXMacroData macro context client

[roberttidball]

Summary

• Add a Python FXMacroData client for macro-aware backtesting and screening workflows.
• Expose FastAPI routes for endpoint discovery, generic FXMacroData requests, and bundled macro context.
• Cover macro data, forecasts, FX, COT, commodities, curves, sessions, risk sentiment, news, press releases, GraphQL, and custom paths.

Tests

• python -m py_compile gunbot_quant/core/fxmacrodata.py gunbot_quant/api/routes.py