style(attachments): apply parser formatting

[seonghobae]

Summary

• apply the repository formatter to the HWP/HWPX attachment parser and focused tests
• keep this PR stacked on feat(attachments): recognize HWP and HWPX parser boundaries #1353 so the feature diff stays isolated

Verification

• ruff format --check backend/services/attachment_parser.py backend/tests/test_attachment_parser.py backend/tests/test_attachment_parser_hwp_signature.py backend/tests/test_attachment_parser_hwpx_bounds.py
• focused attachment parser tests: 99 passed
• git diff --check

Parent PR: #1353

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[seonghobae]

@opencode-agent @cwl-noema-review

Current-head review request for the formatter-only stacked PR #1444.

Exact head: 4f6d91a
Parent/base branch: feat/hwp-hwpx-attachment-recognition at 315ea05

Read the complete four-file diff. Confirm it is formatting-only, remains a safe stack on #1353, introduces no generated or unrelated changes, and preserves the focused HWP/HW/HWPX parser tests. Return a current-head substantive verdict with path:line evidence; do not reuse predecessor evidence or edit/approve from this request.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.