Add FXMacroData price and macro data integration

[roberttidball]

Summary

• keep the FXMacroData daily FX spot downloader and DataProcessor(data_source="fxmacrodata") support
• add FXMacroDataMacroDownloader for announcements, release calendars, forecasts, and catalogue discovery
• add processor helpers for macro data, release calendars, predictions, and joining macro features into RL frames
• update docs and add mocked unit coverage for macro downloads and feature merging

Notes

The macro path exposes FXMacroData's core event surfaces instead of presenting FXMacroData as only a price feed. add_macro_features() can merge announcement values, consensus/forecast fields, surprises, predictions, and release timestamps into price/RL state frames.

Validation

• .venv\Scripts\python -m py_compile finrl\meta\preprocessor\fxmacrodatadownloader.py finrl\meta\data_processors\processor_fxmacrodata.py unit_tests\downloaders\test_fxmacrodata_downloader.py
• .venv\Scripts\python -m pytest unit_tests\downloaders\test_fxmacrodata_downloader.py -q (7 passed, 1 upstream dependency warning)
• .venv\Scripts\python -m black --check finrl\meta\preprocessor\fxmacrodatadownloader.py finrl\meta\data_processors\processor_fxmacrodata.py unit_tests\downloaders\test_fxmacrodata_downloader.py
• git diff --check

Not run locally: pre-commit (module unavailable in the local .venv).