This is a really old module: "Container class for backward compatibility with NumArray" (!)

We should consider deleting it entirely :)

numpy/numpy/tests/test_public_api.py

Line 196 in 06f987b

"lib.user_array", # note: not in np.lib, but probably should just be deleted

Originally posted by @shoyer in #28313

And besides it being very old, a quick code search shows that it's barely used anymore.