`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.

Inizia riproducendo i due snippet dell’issue e ispezionando i test esistenti del restringimento dei tipi o l’implementazione che gestisce i controlli isinstance. Il lavoro è completato quando il primo esempio rileva int e il secondo rileva int | float, oppure il restringimento accettabile documentato, invece di trattare i rami come irraggiungibili.