Put blank lines between nested classes in typing stubs

Describe the style change

Nested classes in typing stubs should have blank lines between them.

Examples in the current Black style

class A:
    class B:
        attribute: int
    class C:
        attribute: int
    def method(self) -> None: ...
    def method2(self) -> None: ...

Desired style

class A:
    class B:
        attribute: int
    
    class C:
        attribute: int
    
    def method(self) -> None: ...
    def method2(self) -> None: ...

Additional context

See this for a live demo.

[JelleZijlstra]

@hauntsaninja we made some changes around that in #2472, but agree that we should space in your example too. Feel free to open a new issue. We also have an unreleased change in #2736.

[JelleZijlstra]

I’m in favor of making this change, but cc fellow typeshed maintainers @srittau @akuli @hauntsaninja.