disallow truncation in types.arraydata

If `types.arraydata` is passed a `numpy.array` with dtype `numpy.int64` and the
platform default int type is 32 bit, then `types.arraydata` truncates the array
to `numpy.int32` without warning. This behavior is inherited from
`numpy.astype`. Since this may lead to unexpected behavior, this patch
disallows truncation by passing `casting='safe'` to `numpy.astype`. Deliberate
truncation should now be done before passing the array to `types.arraydata`.

nutils/types.py

@@ -389,7 +389,7 @@ def __new__(cls, arg):
             return arg
         array = numpy.asarray(arg)
         dtype = dict(b=bool, u=int, i=int, f=float, c=complex)[array.dtype.kind]
-        return super().__new__(cls, dtype, array.shape, array.astype(dtype, copy=False).tobytes())
+        return super().__new__(cls, dtype, array.shape, array.astype(dtype, copy=False, casting='safe').tobytes())
 
     def reshape(self, *shape):
         if numpy.prod(shape) != numpy.prod(self.shape):