feat(lotto): point_in_time_draws 헬퍼

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lotto/tests/test_backtest.py

@@ -60,6 +60,14 @@ def test_random_null_and_coverage_distinct():
     assert len(flat) >= 40   # 커버리지 전략은 번호를 넓게 퍼뜨림
 
 
+def test_point_in_time_excludes_target_draw():
+    draws = _toy_draws(50)   # drw_no 1..50
+    pit = bt.point_in_time_draws(draws, target_draw_no=30)
+    assert all(d < 30 for d, _ in pit)   # 30 이상 제외
+    assert max(d for d, _ in pit) == 29
+    assert len(pit) == 29
+
+
 def test_generate_pool_partial_fill(monkeypatch):
     """weighted_sample_6이 항상 같은 조합만 반환하도록 패치 → cap에 먼저 걸려 len < n — 예외 없이 반환."""
     import random as _r