Refactor operators

[ThexXTURBOXx]

Reviews #115814 (comment), #115814 (comment), and #115814 (comment) show that there are a few things to refactor and/or optimize in regard to operators.
Furthermore, the documentation is sometimes rather hard to read without quotes, such as e.g., "Same as a is None." (which would be much better as "Same as 'a is None'." like @sobolevn proposed).

TODO:

• Optimize C implementations as e.g., shown in gh-115808: Add is_none and is_not_none operators #115814 (comment)
• Rephrase documentation as e.g., shown in gh-115808: Add is_none and is_not_none operators #115814 (comment) and gh-115808: Add is_none and is_not_none operators #115814 (comment)

[sobolevn]

My 2c: the whole module refactoring is usually not-a-so-good idea :)
It might introduce new bugs, it damages the git history and does not bring us much value.

So, let's wait for some other voices: do people find this valuable enough? Or maybe they don't :)

I personally think that adding 'a is None' is a good idea, it make the docs much nicer. But, adding PyBool_FromLong is very optional.

[rhettinger]

I agree with sobolevn that whole module refactoring isn't warranted here. It would be a lot of code churn but offer zero value to the end user.