BUG: converting list of ctypes.Structure to ndarray

[mattip]

Split out of #13399

class Struct(ctypes.Structure):
    _fields_ = [('a', ctypes.c_uint8), ('b', ctypes.c_uint16)]

data = (Struct * 4)()
np.array(data)  # ok
np.array(list(data))
# RuntimeWarning: A builtin ctypes object gave a PEP3118 format string that does not match its itemsize, so a best-guess will be made of the data type. Newer versions of python may behave correctly.
# ValueError: invalid literal for int() with base 10: b'\x00\x00\x00\x00'

We should either correctly parse an iterable of buffers or raise a better error.

[eric-wieser]

For anyone trying to implement this - note that that example is maliciously constructed to run afoul of python/cpython#5561.