Add queue synchronization points in special methods for conversion to scalars

Also synchronize in __sycl_usm_array_interface__ attribute, to ensure
that `dpctl.memory.as_usm_memory(ary).copy_to_host()` produces
expected results.

Author: oleksandr-pavlyk

dpctl/tensor/_usmarray.pyx

@@ -24,7 +24,6 @@ import numpy as np
 
 import dpctl
 import dpctl.memory as dpmem
-import dpctl.utils as du
 
 from .._backend cimport DPCTLSyclUSMRef
 from .._sycl_device_factory cimport _cached_default_device
@@ -82,7 +81,7 @@ cdef class InternalUSMArrayError(Exception):
 cdef object _as_zero_dim_ndarray(object usm_ary):
     "Convert size-1 array to NumPy 0d array"
     mem_view = dpmem.as_usm_memory(usm_ary)
-    du.SequentialOrderManager.wait()
+    usm_ary.sycl_queue.wait()
     host_buf = mem_view.copy_to_host()
     view = host_buf.view(usm_ary.dtype)
     view.shape = tuple()
@@ -519,6 +518,8 @@ cdef class usm_ndarray:
                 "byte_offset is not a multiple of item_size.")
         elem_offset = byte_offset // item_size
         ary_iface['offset'] = elem_offset
+        # must wait for content of the memory to finalize
+        self.sycl_queue.wait()
         return ary_iface
 
     @property