Fix test_io AssertionError

[rajeeja]

E           AssertionError:
E           Not equal to tolerance rtol=1e-08, atol=0
E           Exodus longitude mismatch for RLL1deg
E           Mismatched elements: 63903 / 64442 (99.2%)
E           Max absolute difference among violations: 192.78769181
E           Max relative difference among violations: 10254.862154
E            ACTUAL: array([ 0.,  0.,  1., ..., -2., -1.,  0.], shape=(64442,))
E            DESIRED: array([0.      , 0.      , 0.017457, ..., 0.06987 , 0.017457, 0.      ],
E                 shape=(64442,))

test/grid/grid/test_io.py:148: AssertionError

The error points to _xyz_to_lonlat_rad function producing incorrect results despite correct inputs, suspecting subtle in-place modifications during array operations—possibly from numpy's handling of expressions like x * x. Using python 3.14 and numpy 2.26