121. KS Test Drift Detection

Implement the two-sample KS statistic to detect distribution drift between a reference dataset and a current production dataset.

Signature: def ks_statistic(reference: list, current: list) -> float

The KS statistic is the maximum absolute difference between the empirical CDFs of the two samples evaluated over their combined sorted points.

Example:

• reference = [1, 2, 3, 4, 5]
• current = [3, 4, 5, 6, 7]
• Output: 0.4 (max gap between empirical CDFs)