gh-144330: Initialize classmethod and staticmethod in new (#144469)

Move classmethod and staticmethod initialization from __init__() to
__new__().

PyClassMethod_New() and PyStaticMethod_New() now copy attributes of
the wrapped functions: __module__, __name__, __qualname__ and
__doc__.

Change static type initialization: initialize PyStaticMethod_Type and
PyCFunction_Type earlier.

Remove test_refleaks_in_classmethod___init__() and
test_refleaks_in_staticmethod___init__() tests from test_descr since
classmethod and staticmethod have no __init__() method anymore.