datetime: Comparision and subtraction of datetime objects does not account for DST changes

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

Linked PRs

• gh-146294

America/Los_Angeles ゾーンの zoneinfo の例を使って、文書化された datetime の比較と減算の動作を再現し、datetime.datetime の順序付けと減算のエントリポイントを調査します。結果を timestamp の順序付けおよび記載されたドキュメントのセマンティクスと比較します。DST fold のケース全体で動作とドキュメントが一致し、関連するリグレッションカバレッジがあれば完了です。