[red-knot] Narrowing - Not operator

[TomerBin]

Summary

After #13918 has landed, narrowing constraint negation became easy, so adding support for not operator.

Test Plan

I added a new mdtest file for not expression, but maybe we should spread it over the other test files (by adding not cases to each one of them)? I'll be happy to hear your preference around that :)

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[carljm]

This is awesome, thank you!!

[carljm]

I added a new mdtest file for not expression, but maybe we should spread it over the other test files (by adding not cases to each one of them)? I'll be happy to hear your preference around that :)

I like what you've done here. I think in general any feature that makes sense to make a PR to add, probably makes sense to have a dedicated file to test as well. Which of course isn't incompatible with perhaps also having it occasionally show up in tests of other features, too, but not in a "must add it everywhere" way.