fix: Skylighting code blocks in Typst lack proper block styling

[gordonwoodhull]

Summary

• Override the Pandoc-generated #let Skylighting() Typst function to add width: 100%, inset: 8pt, and radius: 2pt to the block() call, matching native code block styling
• Also fixes brand monospace-block.background-color not applying to Skylighting output (since #show raw.where(block: true) doesn't match #Skylighting() calls)
• This is a temporary workaround until the fix can be upstreamed to the Skylighting library

Fixes #14126

Test plan

• 8 new smoke-all tests covering default, line numbers, brand bgcolor, brand without bgcolor, brand inline, brand+theme, brand+idiomatic, brand inheritance
• 5 pre-existing syntax-highlighting tests still pass
• Visual inspection of rendered Typst PDFs with code blocks

[posit-snyk-bot]

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[gordonwoodhull]

Now using @cderv's suggestion to post-process the Skylighting function in TS instead of using a Lua filter.