fix(muya): preserve fenced code block info string on round-trip (#4770)

[Jocs]

Summary

Fixes #4770. A fenced code block's info string was truncated to its first word when the document was saved:

• ```{example, listing1-name} → ```{example, (a Pandoc/RMarkdown attribute block)
• ```js title="app.js" → ```js (a language followed by attributes)

Root cause

At parse time (markdownToState._buildCodeState) the info string is reduced to its first word for meta.lang, which drives syntax highlighting:

const lang = (infoString || '').match(/\S*/)?.[0] ?? ''

The serializer then emitted only meta.lang, so everything after the first space was lost on save.

meta.lang must stay a single word — the code-block content renderer does wrapper.classList.add(\language-${lang}`), and a langcontaining spaces would breakclassList.add. So widening lang` to the full info string is not an option.

Fix

Preserve the full info string additively in a new optional meta.info, set at parse time only when the info string carries more than the language word, and emit it on serialize:

• meta.lang (first word) still drives highlighting / the language-* class / diagram detection — unchanged.
• meta.info (full string) makes the fence round-trip losslessly.
• Serialization uses meta.info only while lang is still its first word, so editing the language (which rewrites lang) correctly drops the now-stale attributes rather than re-emitting them.

Plain single-word languages and language-less fences produce no meta.info and are byte-identical to before.

Tests

New codeFenceInfoString.spec.ts (markdown → state → markdown round-trip):

• preserves ```{example, listing1-name}
• preserves ```js title="app.js"
• plain ```js and language-less ``` unchanged (no regression)
• an edited language wins over a now-stale stored info string

RED before the fix (both info-string cases truncated), GREEN after. Full muya unit suite (1389), CommonMark/GFM spec conformance (1347), and typecheck all pass.

🤖 Generated with Claude Code