Implement BasicAuth addon that adds following behaviors:
- allows setting credentials via the `.basicAuth()` method
- parses URLs and extracts credentials from them, converting them to an Authorization header and removing them from the URL which would otherwise throw an error when passed to native fetch()
- correctly parses usernames/passwords that contain non-latin characters (see https://developer.mozilla.org/en-US/docs/Glossary/Base64#the_unicode_problem)