More efficient diff function removing quadratic iterable

[KevinMind]

Fixes: mozilla/addons#15170

Testing

Automated test should cover it.. the test without sets hangs forever

Checklist

• Add #ISSUENUM at the top of your PR to an existing open issue in the mozilla/addons repository.
• Successfully verified the change locally.
• The change is covered by automated tests, or otherwise indicated why doing so is unnecessary/impossible.
• Add before and after screenshots (Only for changes that impact the UI).
• Add or update relevant docs reflecting the changes made.

[sentry-io]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: src/olympia/blocklist/mlbf.py

Function	Unhandled Issue
ordered_diff_lists	TypeError: argument of type 'NoneType' is not iterable olympia.blocklist.mlbf in <lis... Event Count: 4

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