Many classes should be decorated as `@final`

While working on several mypy plugins I had often step on the fact you cannot subclass any of the mypy classes, because they are compiled with mypyc. It caused runtime TypeError in the plugin's code.

But, when I was trying to run mypy on the plugin's code - it was fine, no error was shown. Because type are not @final and mypy is not able to understand that this is a problem.

So, I propose to add explicit @final annotations to almost all types, exception:

• Types with allow_interpreted_subclasses
• Types that are subclassed inside mypy itself: Node, Expression, TypeQuery, etc

One more strong point to making this change is that many classes are not "designed" to be subclassed.
So, this should not be a problem.

Related https://github.com/python/mypy/pull/10125
Related https://github.com/python/mypy/pull/9602

L’issue non indica file, test o punti di ingresso. Inizia individuando le definizioni delle classi di mypy e identificando le eccezioni indicate, inclusi i tipi con allow_interpreted_subclasses e le classi derivate all’interno di mypy. Il lavoro è completato quando le classi applicabili sono annotate con @final e il codice del plugin viene verificato di conseguenza.