Add FXMacroData API client

[roberttidball]

Summary

• Add an FXMacroData JSON client under shared/utilities using the project existing CURL dependency.
• Cover macro, FX, COT, commodity, curve, differential, session, news, press release, GraphQL, and custom endpoint requests.
• Add unit coverage with an injectable transport so tests do not call the live API.

Tests

• Added an offline Catch2 test for URL, auth, and body construction.
• Local standalone compile was blocked because this Windows environment does not have curl/curl.h; the project CMake already declares find_package(CURL REQUIRED).

[github-actions]

Thanks for the interest! This repository isn't currently accepting external contributions as I am actively experimenting with different approaches and want to avoid merge conflicts. Therefore, this PR is being closed automatically by Github Bot. See CONTRIBUTING.md for how to fork or file an issue instead.