Update RMM imports to use pylibrmm (#283)

This PR updates the RMM import to use `pylibrmm` now that `rmm._lib` is deprecated . It should be merged after rapidsai/rmm#1676.

Authors:
  - Matthew Murray (https://github.com/Matt711)

Approvers:
  - Peter Andreas Entschev (https://github.com/pentschev)

URL: #283

python/ucxx/ucxx/_lib/libucxx.pyx

@@ -1,4 +1,4 @@
-# SPDX-FileCopyrightText: Copyright (c) 2022-2023, NVIDIA CORPORATION & AFFILIATES.
+# SPDX-FileCopyrightText: Copyright (c) 2022-2024, NVIDIA CORPORATION & AFFILIATES.
 # SPDX-License-Identifier: BSD-3-Clause
 
 
@@ -31,7 +31,7 @@ from libcpp.vector cimport vector
 
 import numpy as np
 
-from rmm._lib.device_buffer cimport DeviceBuffer
+from rmm.pylibrmm.device_buffer cimport DeviceBuffer
 
 from .arr cimport Array
 from .ucxx_api cimport *