Optimize scenario tests: README example test

[MDUYN]

Problem

The README example scenario test in tests/scenarios/test_readme_example.py is currently skipped via @unittest.skip as part of the scenario test optimization effort.

Required changes

1. Reduce execution time — The test dynamically extracts and runs strategy code from README.md, including a vector backtest over a 1.5-year range. Use a shorter date range (e.g. 60–90 days) to keep execution under 30 seconds.

2. Use only offline test data from tests/resources/test_data/ — All data sources must reference CSV files located in tests/resources/test_data/ (or its subdirectories). Tests should not depend on data files scattered across tests/resources/data/ or tests/resources/market_data_sources_for_testing/. This ensures tests are self-contained, reproducible, and don't break when external data files are reorganized.

Affected files

• tests/scenarios/test_readme_example.py

Acceptance criteria

• Test runs in under 30 seconds
• Test uses data exclusively from tests/resources/test_data/
• Remove the @unittest.skip decorator once optimized
• Test passes on both macOS and Ubuntu CI runners