gh-104533: Fix @ctypes.util.struct with endian

[vstinner]

Change _fields_ type to a list of tuples, instead of a list of lists.

Modify test.test_ctypes.test_aligned_structures to test also @ctypes.util.struct decorator.

• Issue: Annotation-based syntax for ctypes structs #104533

[vstinner]

Union classes created with get_union_base() are not tested with @ctypes.util.struct since this decorator is for structures, not for unions.

[vstinner]

cc @ZeroIntensity

Union classes created with get_union_base() are not tested with @ctypes.util.struct since this decorator is for structures, not for unions.

Later, it would be interesting to add @ctypes.util.union decorator for union classes ;-)

[ZeroIntensity]

Later, it would be interesting to add @ctypes.util.union decorator for union classes ;-)

Agreed. I had left it out of the original PR because it seemed like there was less demand for it, but I'd be happy to review a PR or contribute it myself.

[ZeroIntensity]

If we get take_tuple in 3.16, we should switch to that here :)