Add FXMacroData macro data integration

[roberttidball]

Summary

• Adds an FXMacroData integration for the host project's trading/backtesting workflows.
• Covers broad FXMacroData read surfaces: data catalogue discovery, macro announcements, release calendars, predictions, FX rates, COT, commodities, curves, market sessions, risk sentiment, news, press releases, and central-bank context.
• Keeps API-key use optional and query-parameter based so public examples do not require secrets.

Validation

• git diff --check; dotnet build blocked: repo targets .NET 10 but SDK 8/9 installed