Improved on __repr__ of USM memory blobs

```
In [1]: import dpctl.memory as dpm

In [2]: dpm.MemoryUSMShared(64)
Out[2]: <SYCL(TM) USM-shared allocation of 64 bytes at 0x564eb7f30000>
```

Author: oleksandr-pavlyk

dpctl/memory/_memory.pyx

@@ -325,7 +325,7 @@ cdef class _Memory:
 
     def __repr__(self):
         return (
-            "<SYCL(TM) USM-{} allocated memory block of {} bytes at {}>"
+            "<SYCL(TM) USM-{} allocation of {} bytes at {}>"
             .format(
                 self.get_usm_type(),
                 self.nbytes,