PPTX: auto-numbered bullets (buAutoNum) not supported

[developer0hye]

Description

PPTX slides using <a:buAutoNum> (automatic bullet/number lists) lose all list structure during conversion. The numbered items are concatenated into a single text block without line breaks or numbering.

Root Cause

The PPTX parser (crates/office2pdf/src/parser/pptx.rs) does not handle the <a:buAutoNum> element at all — searching for buAutoNum in the parser yields zero matches.

PPTX XML structure:

<a:p>
  <a:pPr indent="-216000">
    <a:lnSpc><a:spcPct val="150000"/></a:lnSpc>
    <a:buAutoNum type="arabicPeriod"/>
  </a:pPr>
  <a:r><a:rPr lang="en-US" sz="2400"/><a:t>Item A</a:t></a:r>
</a:p>
<a:p>
  <a:pPr indent="-216000">
    <a:buAutoNum type="arabicPeriod"/>
  </a:pPr>
  <a:r><a:rPr lang="en-US" sz="2400"/><a:t>Item B</a:t></a:r>
</a:p>

Expected

Each item rendered as a separate numbered line:

1. Item A
2. Item B

Actual

All items concatenated into one block without numbering:

Item AItem B

Scope

Also related: <a:buChar> (custom bullet characters) and <a:buFont> (bullet font) are not handled either. A complete fix should support all three bullet/numbering mechanisms in PPTX text bodies.