Flatten arrays in ravel evaluation

Otherwise it breaks real hard when you try to pass multiple points
into pixel_to_world, because of array broadcasting

dkist/wcs/models.py

@@ -777,6 +777,7 @@ def evaluate(self, *inputs_):
         else:
             has_units = False
             input_values = inputs_
+        input_values = [item.flatten() for item in input_values]
         # round the index values, but clip them if they exceed the array bounds
         # the bounds are one less than the shape dimension value
         array_bounds = np.array(self.array_shape) - 1