save_as_typst: Save flextable objects in a Typst file
Description
Writes one or more flextables to a standalone Typst
(.typ) document. Images are embedded as base64 (decoded inline at
compile time), so the file is self-contained and compiles offline with
typst compile. Equations require the mitex Typst package, which is
fetched from the Typst package registry on first compilation.