[ainuo-AI]

Fixes #190.

When a DNS deliverability check times out or has no usable nameserver, validate_email() returns an accepted address without an mx attribute. A caller following the documented ValidatedEmail.mx API then gets AttributeError instead of None, making it harder to distinguish a temporary lookup problem from a successful check.

Assign mx from the lookup result unconditionally, matching both the README and the existing handling of mx_fallback_type. Make the annotation optional and retain the existing equality behavior with optional MX results. Regression tests exercise the public validator for timeout and no-nameserver outcomes, including as_dict().

The existing report provides a constructed timeout reproduction. I also verified the public API with an ordinary dns.resolver.Resolver pointing only at a bound, nonresponding loopback UDP socket: reading .mx fails before this fix and returns None afterward. This is controlled test data, not a production DNS trace.

Validation:

• Both new regression cases fail before the fix.
• Python 3.14.10, pinned project dependencies: 342 tests pass; the one Internet-dependent test is deselected, as in the project's offline CI test target.
• Official mypy and flake8 checks pass.
• Python 3.12.10: 341 pass and one unrelated IPv4-mapped IPv6 display assertion fails. That same assertion also fails with the original validator implementation; the baseline output is retained locally. This PR leaves that behavior unchanged.

Disclosure: OpenAI Codex assisted with investigation, implementation, tests, and this PR description. No human review or upstream acceptance is claimed.