Relax lxml upper bound to <7

[rolee74]

Why

The current pin lxml>=4.9,<6 makes pip install python-hwpx fail on Python 3.14: lxml 5.x has no prebuilt wheels for 3.14, so pip falls back to a source build (which fails without a libxml2 toolchain). lxml 6.x does ship 3.14 wheels, but the <6 bound excludes it.

Evidence that lxml 6 works

Tested on Windows, Python 3.14.x + lxml 6.0.2 (installed with pip install --no-deps python-hwpx):

• Full test suite: 1274 passed, 0 failed (54 skipped = Hancom Office / macOS oracle tests, 1 xfailed = pre-existing expected failure test_unedited_paragraph_model_roundtrip_is_byte_stable)
• Real-world usage: document authoring via hwpx.authoring Builder API (headings/paragraphs/tables/lists/images), save_to_path() + verify() all green — we ship python-hwpx as an optional dependency of a Claude Code plugin (visionit-harness-kit) for md→hwpx delivery conversion, and currently have to document a --no-deps workaround for 3.14 users.

Change

One line: "lxml>=4.9,<6" → "lxml>=4.9,<7".

(한국어 요약: lxml 5.x 는 Python 3.14 휠이 없어 현재 핀으로는 3.14 에서 설치가 실패합니다. lxml 6.0.2 로 전체 테스트 1274건 통과를 확인해 상한을 <7 로 완화 제안드립니다.)

[airmang]

CI 확인 완료: lxml 6.1.1로 Python 3.10/3.11/3.12에서 mypy·pyright·pytest 모두 통과했습니다. 코드가 사용하는 lxml API는 모두 안정적인 코어 API라 6.x와의 호환 리스크도 없습니다. 감사합니다 🙏