TYP: rec.from{arrays,records} should accept names= without formats= - #31914

Previously, passing names without formats to np.rec.fromarrays and np.red.fromrecords was rejected, even though it's valid at runtime:

In [1]: np.rec.fromarrays([np.array([1., 2.]), np.array([3, 4])], names="a,b")
Out[1]: 
rec.array([(1., 3), (2., 4)],
          dtype=[('a', '<f8'), ('b', '<i8')])

Fully written by me (a human); bug found by Claude Fable 5 (here's the full (second) audit for those interested).

(more stub fixes on the way)