lru_cache variable_names_blacklist_from() logic function

[skarzi]

I have made things!

Checklist

• I have double checked that there are no unrelated changes in this pull request (old patches, accidental config files, etc)
• I have created at least one test case for the changes I have made
• I have updated the documentation for the changes I have made
• I have added my changes to the CHANGELOG.md

Related issues

Closes #1130

To make using lru_cache decorator on variable_names_blacklist_from() possible - _ValidatedOptions has to be hashable, which implies its immutability (I've used attrs frozen argument) that btw is really expected in this case, because configuration options shouldn't be changed after they are loaded and validated.
This change also required updating ConfigurationOptions protocol - all attributes need to be unsettable, because _ValidatedOptions is now frozen/immutable.

If you dislike current solution (personally I don't like new definition of ConfigurationOptions protocol, however according to few issues I have found on mypy repo, it's the only way to define unsettable protocol's attributes) we can change current implementation of variable_names_blacklist_from() a bit, so it will accept allowed_domain_names and forbidden_domain_names immutable arguments instead of _ValidatedOptions, however then _ValidatedOptions will be defined as mutable.

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[coveralls]

Pull Request Test Coverage Report for Build 2532

• 69 of 69 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 2530:	0.0%
Covered Lines:	5106
Relevant Lines:	5106

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💛 - Coveralls

[sobolevn]

Thanks a lot! This is cool!

Do you think that there are possibly other places where caching can be applied?

[skarzi]

Do you think that there are possibly other places where caching can be applied?

I haven't found anything else after quick look on logic/ and visitors/ modules.
But I will remember about checking that during new features/fixes implementation 👍