Bug: DataSource.warmup_window does not propagate to CCXT provider window_size

[MDUYN]

Summary

DataSource.warmup_window does not propagate to the CCXT data provider's window_size parameter, causing backtests to fail when warmup data is requested before the loaded data range.

Current Behavior

When a strategy uses warmup_window on a DataSource, the framework does not pass this value through to the CCXT provider's window_size. As a result, backtests that need warmup data (e.g., for computing indicators like EMA/RSI before the actual backtest start date) fail because the data provider doesn't fetch enough historical data.

Workaround

In tests/scenarios/test_readme_example.py, the README-extracted code replaces warmup_window= with window_size= before executing, which masks the underlying issue:

# Workaround: replace warmup_window with window_size
code = code.replace("warmup_window=", "window_size=")

Expected Behavior

Setting warmup_window on a DataSource should automatically propagate to the underlying data provider (including CCXT) so that sufficient historical data is fetched for indicator warm-up periods.

Steps to Reproduce

1. Create a strategy with a DataSource that uses warmup_window
2. Run a backtest that requires indicator warm-up data before the backtest start date
3. The backtest fails because the CCXT provider doesn't fetch the extra warmup data

Affected Components

• DataSource.warmup_window parameter handling
• CCXT data provider window_size parameter
• Backtest data loading pipeline