[TODO] Get rid of the disabled MyPy error codes

[webknjaz]

1. Go through the disable_error_code entries in .mypy.ini
2. Remove them one by one, and fix whatever they report in the actual Python modules
3. Multiple small PRs are welcome and are preferred over a single gigantic one
4. It should be easier to start with the test modules
5. If there's just one violation in the module, move the disabled error code into that module inline, if it's not fixable
6. If some rules are hard to fix/understand, switch to the easier ones first

[ShubhAgarwal-dev]

Do you know if this issue is still open..? It looks like it has been solved(I followed the conversation on #887)

[webknjaz]

@ShubhAgarwal-dev this is open, the disabled checks are @ https://github.com/aio-libs/multidict/blob/eff79eb/.mypy.ini#L7-L8 and https://github.com/aio-libs/multidict/blob/eff79eb/.mypy.ini#L31-L117.

Typing can be intimidating if you don't have experience already, however. But it's an important skill to have. Just drop the ignores one by one, fixing whatever they reveal. Use pre-commit run mypy-py313 --all-files to see what the disabled check hid once it's re-enabled and fix the typing problem. Repeat for each, but feel free to send PRs fixing subsets of linting violations, no need to do all at once, it can be overwhelming.