Add FXMacroData macro calendar integration

[roberttidball]

Summary

• Adds a TypeScript helper for fetching FXMacroData economic calendar rows and checking event windows.
• Uses the public FXMacroData REST API at https://fxmacrodata.com/api/v1.
• Reads FXMD_API_KEY only when users need authenticated/protected access.

Validation

• Python integration files: python -m py_compile where applicable.
• TypeScript helper: npx tsc --noEmit for BacktestJS.
• git diff --check passed.