feat: support secondary timeframe ingestion

[AKKI0511]

Summary

• extend the data configuration schema and defaults to allow optional secondary timeframes
• update the data loader to cache, resample, and merge secondary timeframe bars into the primary dataset
• add documentation and tests, including an integration test that exercises the pipeline with secondary timeframes

Testing

• poetry run pytest
• poetry run pre-commit run --all-files

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https://chatgpt.com/codex/tasks/task_e_68ef0e5c9a5c832a8b8b617188ac711c