Include humanize_list function as a utility

### What needs to get done

1. Copy this function and its relevant tests to `craft-cli`: https://github.com/canonical/craft-parts/blob/main/craft_parts/utils/formatting_utils.py
2. Make a `craft-cli` release
3. Update craft apps to reference this function instead of their own instances of it.
4. Make comments both here and in the `craft-parts` implementation that the function exists in the other location so we can copy bug fixes if needed. (No functional changes in craft-parts)

### Why it needs to get done

Reduced copy/pasting of code for improved maintainability