mail/py-rfc6555: Happy Eyeballs Algorithm described in RFC 6555 (new port)

Synchronous Python implementation of the Happy Eyeballs Algorithm
described in RFC 6555. Provided with a single file and dead-simple
API to allow easy vendoring and integration into other projects.

PR: 262231
Author: Derek Schrock <dereks@lifeofadishwasher.com>
Differential Revision: https://reviews.freebsd.org/D34389