fix: hide plaintext yuibkey input

[jc12690]

Description (e.g. "Related to ...", etc.)

Utilized getpass() to hide the plaintext when prompted to "insert {key_name} YubiKey and press ENTER." Fix #399.

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• [ ] Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• [ ] Title summarizes what is changing
• [ ] Commit messages are meaningful (see this for details)
• [ ] Tests have been included and/or updated, as appropriate
• [ ] Docstrings have been included and/or updated, as appropriate
• [ ] Changelog has been updated, as needed (see CHANGELOG.md)