Add --verify-data CLI flag, Tensor.data property, parallel DataExecutor

- CLI: --verify-data flag enables Phase 2 data verification (ADR-0020)
- Tensor.data: returns actual numpy values (verify-data) or zeros placeholder
- Tensor.__repr__: shows value summary or data=N/A (placeholder)
- DataExecutor: ThreadPoolExecutor for same-timestamp parallel op execution
- BenchResult.engine: exposes op_log/memory_store for Phase 2 access

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

src/kernbench/runtime_api/context.py

@@ -314,6 +314,7 @@ class RuntimeContext:
         t._handle = handle
         import weakref
         t._ctx_ref = weakref.ref(self)
+        t._memory_store = getattr(self.engine, "_memory_store", None)
         self._tensors.append(weakref.ref(t))
 
         # Install VA→PA mappings via fabric MmuMapMsg