Add fast-path for size == 1 arrays to argsort

Author: ndgrigorian

dpctl/tensor/_sorting.py

@@ -205,6 +205,10 @@ def argsort(x, axis=-1, descending=False, stable=True, kind=None):
         )
     else:
         axis = normalize_axis_index(axis, ndim=nd, msg_prefix="axis")
+    if x.size == 1:
+        return dpt.zeros_like(
+            x, dtype=ti.default_device_index_type(x.sycl_queue), order="C"
+        )
     a1 = axis + 1
     if a1 == nd:
         perm = list(range(nd))