gh-131565: Implement ctypes.util.dllist() in the _ctypes extension (GH-154255)

gh-131565: Implement ctypes.util.dllist() in the _ctypes extension (GH-154255)

On NetBSD dl_iterate_phdr() reports only the link-map group of the calling
object.  Called through ctypes, the caller is libffi's closure trampoline,
which belongs to no object, so only the main executable was reported.
Calling dl_iterate_phdr() from the _ctypes extension module makes _ctypes
the caller and reports all loaded shared libraries.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>