datetime: Comparision does not correctly account for `fold`ed time

[jepler]

Bug report

Bug description:

The documentation of datetime ordering predicates says both that "datetime1 is considered less than datetime2 when datetime1 precedes datetime2 in time, taking into account the time zone" but also "If both comparands are aware, and have the same tzinfo attribute, the tzinfo and fold attributes are ignored"

I believe that ignoring fold, though documented, is incorrect, and contradicts the earlier "precedes ... in time" explanation of what the expression dt1 < dt2 means. If avoiding a conversion to UTC is an important performance optimization, a possibility is to continue to avoid it provided that the fold= and tzinfo= values are the same in both comparands.

>>> from datetime import datetime
>>> import zoneinfo
>>> la = zoneinfo.ZoneInfo("America/Los_Angeles")
>>> t1 = datetime.fromtimestamp(1604221200.0, tz=la)
>>> t2 = datetime.fromtimestamp(1604217660.0, tz=la)
>>> t1 < t2
True
>>> t1.timestamp() < t2.timestamp()
False

Tested on: 3.13.5, 3.15.0a2

CPython versions tested on:

3.15

Operating systems tested on:

Linux

[jepler]

A difficulty is that datetime.time objects ALSO have a fold= attribute. However, as time objects are not associated with a particular moment in time, they cannot be disambiguated by conversion to an unambiguous timestamp. Thus, the suggested logic for comparing datetimes with differing fold attributes cannot be extended to comparing times.

It's tempting to suggest using a simple rule like "the duration of a fold is exactly one hour", but this is not necessarily true. For instance, according to Wikipedia, Lord Howe Island currently applies a 30 minute shift during the summer months.