`not isinstance(float_arg, float)` should narrow to int; `not isinstance(complex_arg, complex)` should narrow to float

The typing specs require that a float typed argument also accept int values, and that a complex type argument accept both int and complex values. That implies that, if we have a val typed complex, and isinstance(val, complex) returns false, it can still be an int or float. So,

def test(x: float):
    if not isinstance(x, float):
        reveal_type(x)  # Should reveal int

and,

def test(x: complex):
    if not isinstance(x, complex):
        reveal_type(x)  # Should reveal int | float (or possibly just float)

But they actually get treated as unreachable code and don't reveal anything.

まず、issue にある 2 つの snippet を再現し、isinstance チェックを処理する既存の型の絞り込みテストまたは実装を調べます。完了条件は、最初の例で int が、2 番目の例で int | float またはドキュメントに記載された許容される絞り込みが明らかになり、分岐が到達不能として扱われないことです。