Fix parsing noon and midnight with AM/PM

[Yananix]

parse_time currently interprets "12:30 AM" as 12:30 and raises ValueError for "12:30 PM" because it adds 12 to an hour that is already 12. This also breaks parsing the strings produced by format_time for midnight and noon in en_US.

Normalize hour 12 to zero when an AM/PM marker is present and the format includes a period, then apply the existing PM offset. Inputs without a period keep their existing interpretation.

Tests cover all 24 hours round-tripping through both the default medium format and an explicit h:mm:ss a pattern, uppercase/lowercase AM/PM at noon and midnight, hour-only input, and 12:30 without a marker.

Validation on macOS with Python 3.12.13 and the repository's CLDR 48.2 data:

• New regression cases: 10 fail before the fix; all 55 pass after it.
• Full pytest suite: 7,885 passed, 7 skipped, 2 xfailed.
• Ruff on both changed files and git diff --check pass.