Add optional argument dns_resolver to validate_email. If provided it will be used instead of the default resolver. The provided resolver can have a configured cache and custom timeout.

Co-authored-by: Joshua Tauberer <jt@occams.info>

…ch expected test results, fixes #60

Check parameter `other` is an instance of ValidatedEmail before
checking all its members are equal to self's members.

…subdomains, except @test when a new test_environment argument is passed

Some of the domain names used in tests had to be revised because they went from valid to invalid, or the exception message changed.

mock.patch("dns.resolver.LRUCache.get") breaks the DNS check in a way that didn't fail the deliverability check before, but it does now, so the mock is replaced with something else.

…racter in the message and add a new test for various unsafe characters

…urrogate code point

…ason

…ommand line