Refine(autofill): Give bonus for exact host match

[maederm]

Hi @keepassium

I know that you don't accept PRs, but maybe this inspires you to add a ranking bonus for exact domain matches.
This PR doesn't account for protocol.

• Move howSimiliar into library to make it unit testable
• Add unit tests for different matching cases
• Add build/ folder to .gitignore

Fixes #480

Disclaimer: The code changes were mostly generated with AI tooling. I verified the output of the addition to the similarity logic. The unit tests look good to me, but I’m not sure if you’d write them like that. In pytest I would use parametrize for example. I ran the unit tests successfully in the simulator and also verified that they fail if I change the code.
I didn’t change the copyright headers as most of the logic was already there.

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