Three new tests for the naive timestamp fix (PR #807):
- test_ensure_aware_naive_preserves_absolute_time: verifies UTC equivalent
is preserved when interpreting naive datetimes as system-local time
- test_ensure_aware_normalizes_aware_to_hermes_tz: verifies already-aware
datetimes are normalized to Hermes tz without shifting the instant
- test_ensure_aware_due_job_not_skipped_when_system_ahead: end-to-end
regression test for the original bug scenario