feat(xlsx): print worksheet gridlines when printOptions asks for them

[developer0hye]

Summary

<printOptions gridLines="1"/> prints Excel's worksheet gridlines across the printed range; the attribute was never read, so grid-structured sheets came out with no rules at all.

Measured off the native Excel GT of NumberFormatTests (traces cited in the code): printed gridlines are 1pt pure-black boundary-anchored [B, B+1] bands — the #619 thin-border convention, not the commonly assumed gray — covering exactly the printed range, closed on all four sides at every page break. An explicit border of any style owns its boundary over the gridline (a hair border replaces the black rule with its dotted band), and a cell fill suppresses all four adjacent segments (Excel truncates verticals at a filled row and omits the horizontal at its bottom edge).

Implementation seeds gridline declarations into the #619 boundary-resolution pass (lowest precedence, both-neighbour seeding so grids close at page breaks), riding the existing band emission including repeating headers and width splits. The flag is read by a raw-XML scanner that skips customSheetViews subtrees (a custom view's nested printOptions must not shadow the sheet-level element) and honours the ECMA-376 gridLines AND gridLinesSet conjunction; umya models neither attribute.

Known limitation (TODO in code): a background-filled row that lands as the first row of a page leaves the previous page's grid open at that one boundary — kept because the alternative paints a black rule over the fill's top edge on every within-page filled row, the far more common case.

Related issue

Fixes #622

Testing

• cargo test --workspace — green (red-first tests: measured band geometry on all four sides, both-neighbour interior seeding, explicit-border precedence incl. hair, fill suppression, repeating-header carry, flag-off negatives; scanner tests for customSheetViews shadowing both directions, gridLinesSet veto, "true" spelling)
• cargo +1.97 clippy --workspace --all-targets — clean; cargo fmt --check — clean
• GT parity on NumberFormatTests: every rule 1.0pt #000000 at boundary bands matching GT's fills; fill suppression mirrored; pages closed top and bottom; Flags-sheet variable-height rows match GT offsets
• Perf: conversion 474ms → 547ms (+15%) with ~5,400 added bands; parse time unchanged

Visual impact

• No rendered PDF change
• Rendered PDF change or visual evidence added
• Reason:

Visual audit

• Issue: XLSX: printOptions gridLines="1" is ignored, so printed cell gridlines are missing entirely #622
• Fixture: tests/fixtures/xlsx/poi/NumberFormatTests.xlsx
• Page(s): Tests sheet page 1 (output page 2; GT page dimensions differ per open XLSX: an omitted pageSetup paperSize falls back to A4 instead of the schema-default Letter, so a Letter workbook prints 16.7pt narrow and 49.9pt tall #717 — Letter vs A4)
• Renderer and DPI: pdftoppm, 150 DPI
• Evidence mode: fix
• New follow-up issues found in this audit: None
• GT: assets/bugfixes/issue-622/gt.jpg
• Before: assets/bugfixes/issue-622/before.jpg
• After: assets/bugfixes/issue-622/after.jpg

Visual comparison

GT	Before	After

Required inspection

• Rendered all evidence at 150 DPI or higher
• Stored progressive JPEG quality 86 assets with metadata stripped
• Inspected matched region crops at full resolution
• Ran the 5% fuzz pixel-difference sweep
• Inventoried hairlines and border dash styles
• Inventoried font weight, italic, and underline emphasis

Deviation audit

Check	Result
Page count/order	Remaining: #658 — 12pt rows vs GT 13pt pull ~7 extra rows onto page 1; Remaining: #717 — A4 page vs GT's schema-default Letter
Element presence	Remaining: #623 — row/column heading gutters and the outer heading frame are absent; Remaining: #718 — the formatted empty column E (gridlines and fill segment included) is absent
Position/size	Remaining: #623 — the cell area sits at the page origin instead of after GT's heading gutter; column boundaries align exactly once shifted, and column widths match GT within 1px
Rotation/flip	No deviation observed
Fill	Matches GT — header fill #FFCC99 identical over A1:D1; the missing E1 segment is tracked under #718
Stroke/border	Fixed — printed gridlines now appear as 1pt pure-black rules (2px at 150 DPI, same bands as GT) across the whole range, with GT's fill-edge suppression reproduced; before: zero rules on the page
Text content	Remaining: #719 — rows 44–46 drop the xml:space="preserve" leading spaces; all other text matches
Font family/weight/style	Matches GT — italic sans header + regular monospace body
Text color	Matches GT — black throughout
Alignment	Remaining: #657 — left-aligned text at 2.6pt from the rule vs GT 3.6pt (the 1pt inset deficit); right alignment matches
Line/paragraph spacing	Remaining: #658 — uniform 12pt row pitch vs GT 13pt
Clipping/overflow	No deviation observed

Checklist

• Commits include a Signed-off-by line
• PR scope contains one root cause
• Remaining visual deviations each reference an open issue

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