Remove _SynchronousMemoryResource from cuda.core._memory public API

Remove _SynchronousMemoryResource from __all__ in _legacy.py since it is
a private symbol (underscore-prefixed) that should not be part of the
public API surface.

Update internal imports in _device.pyx and test_launcher.py to use the
full private module path (cuda.core._memory._legacy) instead of the
package-level import.

Author: mdboom

cuda_core/cuda/core/_device.pyx

@@ -1145,7 +1145,7 @@ class Device:
                 from cuda.core._memory import DeviceMemoryResource
                 self._memory_resource = DeviceMemoryResource(self._device_id)
             else:
-                from cuda.core._memory import _SynchronousMemoryResource
+                from cuda.core._memory._legacy import _SynchronousMemoryResource
                 self._memory_resource = _SynchronousMemoryResource(self._device_id)
 
         return self._memory_resource

cuda_core/cuda/core/_memory/_legacy.py

@@ -1,4 +1,4 @@
-# SPDX-FileCopyrightText: Copyright (c) 2024-2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-FileCopyrightText: Copyright (c) 2024-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 #
 # SPDX-License-Identifier: Apache-2.0
 
@@ -17,7 +17,7 @@
     driver,
 )
 
-__all__ = ["LegacyPinnedMemoryResource", "_SynchronousMemoryResource"]
+__all__ = ["LegacyPinnedMemoryResource"]
 
 
 class LegacyPinnedMemoryResource(MemoryResource):

cuda_core/tests/test_launcher.py

@@ -24,7 +24,7 @@
     ProgramOptions,
     launch,
 )
-from cuda.core._memory import _SynchronousMemoryResource
+from cuda.core._memory._legacy import _SynchronousMemoryResource
 from cuda.core._utils.cuda_utils import CUDAError