* Add a native _zoneinfo module
ZoneInfo reads TZif tuples from zoneinfo._common.load_data. The stdlib
module implements utcoffset, dst, tzname, fromutc, and the zone cache.
whats_left compares that class. Cache tests no longer expect failure.
Assisted-by: Grok:grok-4.7
* Fix ZoneInfo layout and keep its cache on the module
utcoffset, dst, and tzname take the object. Zone data is boxed so the
payload lines up with tzinfo on 32-bit. The strong, weak, and timedelta
caches live on each interpreter's _zoneinfo module.
Assisted-by: Grok:grok-4.7
