chore(nargo)!: restrict CliError visibility to crate

[TomAFrench]

Related issue(s)

Followup to #907

Description

Summary of changes

CliError shouldn't be made public so I've adjusted its visibility to ensure that it stays only visible within the crate. I've had to adjust the visibility of other functions to match (we don't change the crate's interface doing this however).

This PR is technically breaking as we've removed the check_from_path from the crate interface.

Dependency additions / changes

Test additions / changes

Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt with default settings.
• I have linked this PR to the issue(s) that it resolves.
• I have reviewed the changes on GitHub, line by line.
• I have ensured all changes are covered in the description.
• This PR requires documentation updates when merged.

Additional context