feat(v2): complete v2 reimplementation

tests/unit/test_cron_dst.py

@@ -0,0 +1,18 @@
+from __future__ import annotations
+
+from datetime import UTC, datetime
+
+import pytest
+from backup_tool.scheduler import ScheduleError, next_nominal
+
+
+def test_five_field_cron_returns_utc_nominal_time() -> None:
+    result = next_nominal("0 9 * * *", "America/New_York", datetime(2026, 1, 1, tzinfo=UTC))
+    assert result.tzinfo is UTC
+    assert result.hour == 14
+
+
+@pytest.mark.parametrize(("cron", "timezone"), [("* * * * * *", "UTC"), ("* * * * *", "Nope/Zone")])
+def test_invalid_cron_or_timezone_is_rejected(cron: str, timezone: str) -> None:
+    with pytest.raises(ScheduleError):
+        next_nominal(cron, timezone)