According to the docs and comment inside module_copy_string_contents it
should always produce a valid utf-8 string that can be used in dynamic
modules, but it seems it's not always the case. I encountered an emacs
crash when using emacs-module-rs because it always expects a valid utf-8
for strings. To reproduce you can call:

(some-function-from-dynamic-library (encode-coding-string (f-read-text
"wg-private-pc.age") 'utf-8 t))

The file is
https://github.com/kurnevsky/nixfiles/raw/0b3de016dac551398627a55788b80d4809afcbf9/secrets/wg-private-pc.age

See https://github.com/ubolonton/emacs-module-rs/issues/58 for additional
details.