`__bool__` should fall back to `__len__` when it is undefined

[tatyam-prime]

Hello! I'm trying to use Codon.

According to https://docs.python.org/3.13/reference/datamodel.html#object.__bool__, if a class does not define __bool__, Python should call __len__ to determine truthiness.

However, in Codon 0.19.3, attempting to evaluate such an object in a boolean context causes an error.

Example:

class A:
    def __len__(self) -> int:
        return 0

a = A()
print(bool(a))

This should output:

False

But Codon raises an error:

bool.codon:12 (16-31): error: 'A' object has no attribute '__bool__'
╰─ Main.py:6 (7-14): error: during the realization of __new__(what: A)

[tatyam-prime]

Also, __ne__ should fall back to __eq__.