fix(xlsx): read self-closing drawing run properties

[developer0hye]

Summary

• extract the <a:rPr> attribute loop into apply_run_properties
• call it from the reader's Event::Empty arm as well as Event::Start, so a self-closing <a:rPr/> keeps its size, bold, and italic

Related issue

Fixes #466

Details

Excel writes a shape label's run properties as a self-closing element, <a:rPr lang="en-US" sz="1100"/>, which quick-xml reports as Event::Empty. The drawing reader matched rPr only in its Event::Start arm, so every attribute on that spelling was discarded and the run fell back to the renderer's default 11pt regular.

That default happens to equal the common sz="1100", which hid the defect until a label used another size or weight. Parsing the same attributes in both spellings showed the split:

Run properties	font_size	bold	italic
<a:rPr lang="en-US" sz="1400" b="1" i="1"/>	None	None	None
<a:rPr … ><a:solidFill>…</a:solidFill></a:rPr>	Some(14.0)	Some(true)	Some(true)

Only the presence of a child element changed the outcome, which is not a distinction DrawingML makes. The new tests assert both spellings resolve identically, and that b="0"/i="0" still mean "not bold"/"not italic".

Testing

• cargo fmt --all -- --check
• cargo test --workspace
• cargo clippy --workspace --all-targets --all-features
• rendered all 68 committed XLSX fixtures before and after and compared pdftotext -bbox output

Visual impact

• No rendered PDF change
• Rendered PDF change or visual evidence added
• Reason: no committed fixture exercises the defect. The only self-closing run properties in the corpus use sz="1100", which equals the renderer default. Rendering all 68 XLSX fixtures before and after leaves 67 byte-identical in pdftotext -bbox layout; the 68th (tests/fixtures/xlsx/WithDrawing.xlsx) differs only by 1e-5 pt on two word coordinates, from taking Typst's explicit-11pt path instead of its default-11pt path. Documents outside the corpus that use another size, bold, or italic on a self-closing <a:rPr/> will render differently — correctly — after this change.

Checklist

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