Possible bug in GridInterpolator (with suggested fix)

I think there is a possible bug in GridInterpolator in v2.3.0, but there is an easy fix 😄

x = [np.array([0.0, 2.99999, 3.0, 3.5, 4.0, 4.5]),
     np.array([0.84, 0.85, 0.86, 0.87, 0.88, ])
    ]
V = np.reshape(np.array(range(30)), (6, 5))

Instantiating the interpolator the first time works ok

GridInterpolator(x, V)
<py_wake.utils.grid_interpolator.GridInterpolator at 0x1bfdf918250>

But if instantiated twice in a row (such as with PowerCtNDTabular), then an error occurs because the original x has been changed

GridInterpolator(x, V)
ValueError: Lengths of x does not match shape of V

x
[array([0.     , 2.99999, 3.     , 3.5    , 4.     , 4.5    , 5.5    ,
        6.5    ]),
 array([0.84, 0.85, 0.86, 0.87, 0.88])]

The simple fix for this is to edit the init of GridInterpolator such that it always works on a copy:

self.x = x.copy()