This PR updates the documentation for datetime and zoneinfo to clarify how arithmetic involving aware datetime objects behaves during daylight saving time (DST) transitions.

Changes include:

• A .. warning:: in the timedelta section noting that arithmetic on aware datetime objects with the same tzinfo ignores DST.
• A .. note:: in the datetime subtraction section, with a concrete example, explaining the "naive time" behavior.
• A correction to the misleading sentence in zoneinfo.rst that previously claimed "no further intervention" was required to handle DST transitions.
• A corresponding .. note:: in zoneinfo.rst to show how timedelta arithmetic skips DST transitions unless handled explicitly.

This PR resolves gh-116111 based on the suggestions on the issue

📚 Documentation preview 📚: https://cpython-previews--137092.org.readthedocs.build/