Support 'on'/'off' for type ignores

Sometimes it's impossible to put # type: ignore on the offending line - e.g. because it's a multiline string, and there's nowhere you can put the comment outside the string that mypy will recognise. Or more generally, there might be a whole block of code for which mypy has a bunch of spurious complaints, so putting in dozens of # type: ignores is a bit noisy.

The only other option today is to have mypy ignore the entire file, but that has nasty ramifications - beyond just killing type checking for what might be 99% checkable, it also makes any imports of that file invalid, and so you have to spread ignore directives out like a messy spiderweb.

Thus, it'd be great if one could do e.g. # type: ignore on and # type: ignore off, so that the scope could be controlled precisely.

Das Issue nennt keine Dateien, Tests oder Einstiegspunkte. Beginne damit nachzuverfolgen, wie mypy derzeit # type: ignore-Direktiven parst und anwendet, und bestimme dann, wie on und off Diagnosen über mehrzeilige Zeichenketten und Codeblöcke hinweg begrenzen sollen. Erledigt ist die Aufgabe, wenn bereichsbezogene Ignores funktionieren, ohne die Prüfung für den Rest der Datei zu deaktivieren oder Importe ungültig zu machen.