Add FXMacroData calendar example

[roberttidball]

Summary

• Adds FXMacroData calendar Go example for using FXMacroData's public release-calendar endpoint in backtesting or strategy-risk workflows.
• Keeps the integration self-contained and avoids API-key requirements by using the public USD calendar example.

Validation

• Ran Python syntax checks for all added Python examples where applicable.
• Ran git diff --check for this repository.
• Live FXMacroData calendar smoke tested with the July 2026 USD sample window from companion Python examples.

Note: Go, Rust, .NET, Maven, and TypeScript toolchains were not available in the local desktop environment for deeper build checks.

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.97%. Comparing base (7cba43f) to head (047e3fa).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #390      +/-   ##
==========================================
+ Coverage   91.92%   91.97%   +0.05%     
==========================================
  Files         229      229              
  Lines        7231     7231              
==========================================
+ Hits         6647     6651       +4     
+ Misses        494      490       -4     
  Partials       90       90              

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[roberttidball]

I have read the CLA Document and I hereby sign the CLA

[roberttidball]

recheck