fix(core): retain driver log buffers for CUlinkState lifetime

Linker_link was nulling self._drv_log_bufs right after cuLinkComplete,
releasing the bytearrays whose addresses were handed to the driver via
CU_JIT_INFO_LOG_BUFFER and CU_JIT_ERROR_LOG_BUFFER at cuLinkCreate time.
The CUlinkState retains those pointers until cuLinkDestroy, which runs
during Linker tp_dealloc. Freeing the bytearrays first left the driver
with dangling pointers and corrupted the heap; subsequent CUDA calls
(e.g. NVRTC compilation in the next test fixture) segfaulted.

This path became reachable in CI with the new per-instance backend
dispatch: CTK 12.9.1 + driver 13.0 runners now hit the driver linker
for cross-major linking, which was never exercised before.

Retain _drv_log_bufs until the cdef class is deallocated; pxd
declaration order ensures _culink_handle (and therefore cuLinkDestroy)
runs before the bytearrays are cleared.

Author: cpcloud

cuda_core/cuda/core/_linker.pxd

@@ -10,7 +10,7 @@ cdef class Linker:
         NvJitLinkHandle _nvjitlink_handle
         CuLinkHandle _culink_handle
         bint _use_nvjitlink
-        object _drv_log_bufs  # formatted_options list (driver); None for nvjitlink; cleared in link()
+        object _drv_log_bufs  # formatted_options list (driver); None for nvjitlink
         str _info_log         # decoded log; None until link() or pre-link get_*_log()
         str _error_log        # decoded log; None until link() or pre-link get_*_log()
         object _options       # LinkerOptions

cuda_core/cuda/core/_linker.pyx

@@ -627,11 +627,12 @@ cdef inline object Linker_link(Linker self, str target_type):
             raise
         code = (<char*>c_cubin_out)[:c_output_size]
 
-    # Linking is complete; cache the decoded log strings and release
-    # the driver's raw bytearray buffers (no longer written to).
+    # Linking is complete; cache the decoded log strings. The driver's raw
+    # bytearray buffers are retained for the lifetime of the CUlinkState
+    # because cuLinkDestroy may still dereference the log-buffer pointers
+    # registered via cuLinkCreate.
     self._info_log = self.get_info_log()
     self._error_log = self.get_error_log()
-    self._drv_log_bufs = None
 
     return ObjectCode._init(bytes(code), target_type, name=self._options.name)