The problem is not what I care, but I read your README and I knew it from my knowledge.

The Thin space (in Typst, it is represented by\u{2009}) can be used for space between numbers and SI units. To use it, we can define some functions for Typst similar to those available in siunitx.

• Graphic designers are oftenly using "thin space" if the "space" is not good.
• The default breaks between value and units is \u{2009} from siunitx-v2.sty
• If there is a very long long long sentence, Typst will break a thin space, whill LaTeX will not. And, Typst follows the Unicode Standard.

This is still a unicode trick, but works in Typst...

Reference:

• an awesome blog post: Adventures in space: Spaces
• Whitespace character - Wikipedia

  Thin space; one-fifth (sometimes one-sixth) of an em wide. Recommended for use as a thousands separator for measures made with SI units. Unlike U+2002 to U+2008, its width may get adjusted in typesetting.[3] HTML/XML named entity:  ,  , LaTeX: \, (the LaTeX thin space is a no-break space)

• The Unicode Standard 5.0, printed edition, Chapter 6, Space Characters

  The exception is U+2009 thin space, which sometimes gets adjusted.