Make copy argument of __array__ method keyword-only

dpctl/tensor/_usmarray.pyx

@@ -1552,8 +1552,15 @@ cdef class usm_ndarray:
     def __repr__(self):
         return usm_ndarray_repr(self)
 
-    def __array__(self, dtype=None, copy=None):
-        "NumPy array protocol"
+    def __array__(self, dtype=None, /, *, copy=None):
+        """NumPy's array protocol method to disallow implicit conversion.
+
+	Without this definition, `numpy.asarray(usm_ar)` converts
+	usm_ndarray instance into NumPy array with data type `object`
+	and every element being 0d usm_ndarray.
+
+        https://github.com/IntelPython/dpctl/pull/1384#issuecomment-1707212972
+	"""
         raise TypeError(
             "Implicit conversion to a NumPy array is not allowed. "
 	    "Use `dpctl.tensor.asnumpy` to copy data from this "