tests: add memory_ipc/__init__.py to avoid conftest module collision

Without __init__.py in tests/memory_ipc/, pytest imports
tests/memory_ipc/conftest.py under module name `conftest`, which collides
with the top-level tests/conftest.py. Tests under tests/ that use
`from conftest import X` then resolve to the wrong file at import time,
yielding ImportErrors like:

    ImportError: cannot import name 'skipif_need_cuda_headers' from
    'conftest' (.../tests/memory_ipc/conftest.py)

The fix mirrors tests/system/ (which already has both __init__.py and
conftest.py): adding tests/memory_ipc/__init__.py makes memory_ipc a
proper package, so its conftest is imported as memory_ipc.conftest and
the top-level conftest stays under name `conftest`.

Author: Andy-Jost

cuda_core/tests/memory_ipc/__init__.py

@@ -0,0 +1,3 @@
+# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+#
+# SPDX-License-Identifier: Apache-2.0