Prefer getpass.getuser() over os.getlogin() as noted in the official docs.

This fixes the following error when running within a Debian container in GitHub codespaces:

>>> import os
>>> os.getlogin()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 6] No such device or address

• Tests pass
• Tests and examples for any new features.
• Appropriate changes to README are included in PR