Fix local timezone offsets in get_timezone_name(None)

[arindamsikder]

Summary

Preserve the local timezone when resolving get_timezone_name(None), including its GMT-offset fallback and daylight-saving-time selection.

Problem

The None path creates a naive local datetime. If there is no translated timezone name, get_timezone_gmt() treats that datetime as UTC, so a local offset such as GMT+05:30 becomes GMT+00:00. This causes the existing test_get_timezone_name_misc regression to fail outside UTC.

Solution

• Construct the current datetime with LOCALTZ attached through datetime.now(LOCALTZ).
• Read DST from the resulting datetime rather than asking the original timezone object to localize it again. This also handles pytz's localized timezone objects.
• Correct the None parameter documentation to reflect the established local-time behavior.
• Add deterministic positive/negative fixed-offset and winter/summer regression coverage for pytz and zoneinfo.

No timezone database, public API, dependency, or workflow changes.

Testing

Executed on Linux/Python 3.11 in a credential-free, network-isolated Bubblewrap environment:

• New regression tests on the unchanged base: 6 failed for the expected incorrect offset/naive datetime behavior; the same tests pass with the fix.
• TZ=UTC make test PYTEST_FLAGS='-p no:cacheprovider --basetemp=/tmp/pytest': 7,837 passed, 7 skipped, 2 xfailed. One existing pytest deprecation warning remains.
• tests/test_dates.py under both UTC and Asia/Kolkata: 2,390 passed, 2 xfailed in each run.
• Independent read-only automated review reran the dates, date/time formatting, intervals, support-formatting and localtime suites under UTC, America/New_York and Asia/Kolkata: 2,457 passed, 2 xfailed in each run.
• Independent zoneinfo-only runs (pytz imports disabled) under UTC and America/New_York: 1,289 passed, 1,169 skipped, 1 xfailed in each run.
• Additional independent probes exercised named/fixed zones, DST transitions, positive/negative offsets, explicit and generic inputs, widths, zone variants and return_zone; no compatibility regression was found.
• Pinned Ruff 0.14.10: ruff check --no-cache babel/dates.py tests/test_dates.py passed.
• git diff --check passed.

The full supported-Python/OS CI matrix was not run locally; upstream CI and maintainer review are still required.

Related Issue

Fixes #935.

Automation disclosure

Prepared by the Hermes autonomous engineering agent operated by Arindam Sikder (@arindamsikder), with a separate read-only automated reviewer that independently executed tests against the exact patch. This is not a claim of human maintainer approval. No automatic merge is requested or performed.

Base: e2a17919f0eb988bfea2883b00793ca4d5d37c4f
Head: 5a68e8668b6e549a3f2e6571838455978f453ef2

[akx]

This is a behavioral change, isn't it?