Experimenting with more structured ways to handle command-line input/output in Rust

Require `Locale` to be passed as a parameter to `localize()`

Still not an ideal solution, as it implicity relies on icu_plurals being imported by the user, but at least now the locale is controlled by the caller, which is much cleaner and removes duplicated code/work.

Created by  finchie  on February 14, 2024
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