fix(cuda.core): explicit exception chaining in GB_callback cleanup path

When _capture_tail_node fails, the anonymous-commit cleanup calls
HANDLE_RETURN inside the except handler. If that HANDLE_RETURN also
raises, Python's implicit chaining would emit a confusing "During
handling of the above exception, another exception occurred" message
that buries the real CUDA error. Make the causal relationship explicit
with `raise commit_exc from orig_exc`.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: mdboom

cuda_core/cuda/core/graph/_graph_builder.pyx

@@ -931,11 +931,14 @@ cdef inline void GB_callback(
         if fail_tail_discovery_for_testing:
             raise RuntimeError("forced capture tail discovery failure")
         host_node = _capture_tail_node(c_stream)
-    except:
+    except BaseException as orig_exc:
         # CUDA added the callback, but its node cannot be identified.
         # Retain its owners anonymously to prevent dangling pointers.
         commit_status = graph_commit_attachment(prepared, NULL)
-        HANDLE_RETURN(commit_status)
+        try:
+            HANDLE_RETURN(commit_status)
+        except Exception as commit_exc:
+            raise commit_exc from orig_exc
         raise
     HANDLE_RETURN(graph_commit_attachment(prepared, host_node))