`isinstance` check with nested `Protocol`.

isinstance(obj, ProtocolSubclass) only checks the the existence of ProtocolSubclass's methods on obj and not the type signature. To provide deeper checks, maybe isinstance could check attributes/methods on ProtocolSubclass that are themselves a Protocol.

A small example showing the change in behavior:

@runtime_checkable
class FooLike(Protocol):
    attr: str

@runtime_checkable
class BarLike(Protocol):
    attr: FooLike

@dataclass
class Foo:
    attr: str = "test"

@dataclass
class Bar:
    attr: Foo

foo = Foo()
bar = Bar(foo)

# No change in current behavior
assert isinstance(foo, FooLike)  # passes
assert isinstance(bar, BarLike)  # passes
assert isinstance(bar, FooLike)  # passes

# Change in behavior
assert not isinstance(foo, BarLike)  # NOT because `BarLike.attr` should be `FooLike` and `foo.attr` is not

Comienza con el comportamiento en tiempo de ejecución de isinstance(obj, ProtocolSubclass) y los ejemplos de @runtime_checkable Protocol del informe. Compara las comprobaciones superficiales actuales de existencia de atributos con el comportamiento anidado de Protocol solicitado y, después, usa las assertions del ejemplo para definir la finalización.