feat(definition-list): render definition lists to <dl>/<dt>/<dd>

[lolifamily]

Closes #106

Add a definitionList feature (off by default) following the pandoc / PHP Markdown Extra syntax: a term line followed by one or more colon-marked definitions parses into new descriptionList, descriptionTerm, and descriptionDetails mdast nodes, rendered as <dl>/<dt>/<dd>.

• Tight vs loose is tracked per definition: spread lives on each descriptionDetails (mirroring mdast-util-definition-list), so a loose <dd> keeps its inner <p> while a tight one unwraps it, reusing the existing list-item paragraph-unwrap path.
• The definition marker only claims a lone colon, so a ::/::: fence still parses as a directive when both extensions are enabled. Covered by dedicated regression tests for the colon interaction.
• The three nodes are wired through the full pipeline: layout-codegen registry, walk/reader decoders, plugin visitor keys, prop slots, and the op-stream round-trip, plus features / plugin-api docs.

This also replaces the earlier stub that mapped definition-list syntax onto nested paragraphs, fixing the malformed <p><p>...</p></p> output in the #949 regression snapshots.

The build additionally refreshes the checked-in napi bindings (index.js, wasi-worker-browser.mjs), which had drifted to 0.8.1 while the package is already at 0.9.4 — an incidental artifact refresh, not a functional change.

[codspeed-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks
⏩ 8 skipped benchmarks¹

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_{Comparing lolifamily:feat/definition-list (5c4a5db) with main (ef3974e)}

Footnotes

1. 8 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩