Fix access violation in occupancy queries with uninitialized hStream

Zero-initialize CUlaunchConfig struct to prevent garbage values in
hStream field when no stream is provided. The driver dereferences
hStream even when querying occupancy, causing access violations on
some platforms (observed on Windows with RTX Pro 6000).

Author: Andy-Jost

cuda_core/cuda/core/_launch_config.pyx

@@ -2,6 +2,8 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
+from libc.string cimport memset
+
 from cuda.core._utils.cuda_utils cimport (
     HANDLE_RETURN,
 )
@@ -139,9 +141,9 @@ cdef class LaunchConfig:
 
     cdef cydriver.CUlaunchConfig _to_native_launch_config(self):
         _lazy_init()
-        # TODO: memset to zero?
         cdef cydriver.CUlaunchConfig drv_cfg
         cdef cydriver.CUlaunchAttribute attr
+        memset(&drv_cfg, 0, sizeof(drv_cfg))
         self._attrs.resize(0)
 
         # Handle grid dimensions and cluster configuration