Enable type checking of `tomllib` stdlib folder

[sobolevn]

Following example of #131509 I propose to add mypy type checking in CI for tomllib.

It is fully typed already, we just need to run the CI if something changes.

Linked PRs

• gh-133117: Run mypy on tomllib in CI #133118
• [3.13] gh-133117: Run mypy on tomllib in CI (GH-133118) #133192
• gh-133117: Enable stricter mypy checks for tomllib #133206
• [3.13] gh-133117: Enable stricter mypy checks for tomllib (GH-133206) #133343

[AA-Turner]

cc @hukkin.

See also discussion in #128907 re possibly removing annotations from tomllib in the future (post 3.10 EOL) for performance/etc. Given that's a way off though, running mypy may be pragmatic in the meantime.

A

[hukkin]

I fully support this.