Correctly handle and validate SPF macros in mechanisms and modifiers (#218)

* Apply macro validation to all mechanisms and modifiers that support it and stop processing them further, since macros can only be validated in the context of an actual email.

* Fix formatting and import statements in spf.py

* Revert shitty AI merge

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Co-authored-by: Ebrahim Aharpour <ebrahim@kevlarr.io>
Co-authored-by: Sean Whalen <44679+seanthegeek@users.noreply.github.com>

Author: 3 people