Fold-ambiguous datetimes break == and same-tz subtraction in tests

Two datetime behaviours make DST tests give false results. First, inter-zone == always returns False if either side is in a repeated hour: datetime(2026,11,1,1,30,tzinfo=NY) == datetime(2026,11,1,5,30,tzinfo=timezone.utc) is False even though they are the same instant. Convert both sides with .astimezone(timezone.utc) before comparing. Second, subtracting two datetimes that share the same tzinfo ignores offset and fold, so 1:30 EDT minus 1:30 EST (fold=1) gives 0:00:00 instead of 3600 seconds. Measure elapsed seconds with b.timestamp() - a.timestamp() or by subtracting UTC-converted values, and set fold=1 to mean the second (standard-time) occurrence.