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>

tests/test_cli_verify_data.py

@@ -0,0 +1,49 @@
+"""Tests for --verify-data CLI flag (Phase 1 verification)."""
+import kernbench.cli.main as cli_main
+
+
+def test_cli_verify_data_flag_parsed(monkeypatch):
+    """--verify-data flag is parsed and stored as True."""
+
+    def fake_cmd_run(args) -> int:
+        assert args.verify_data is True
+        return 0
+
+    monkeypatch.setattr(cli_main, "cmd_run", fake_cmd_run)
+    rc = cli_main.main([
+        "run", "--topology", "topology.yaml", "--bench", "qkv_gemm",
+        "--verify-data",
+    ])
+    assert rc == 0
+
+
+def test_cli_verify_data_flag_default(monkeypatch):
+    """Without --verify-data, flag defaults to False."""
+
+    def fake_cmd_run(args) -> int:
+        assert args.verify_data is False
+        return 0
+
+    monkeypatch.setattr(cli_main, "cmd_run", fake_cmd_run)
+    rc = cli_main.main([
+        "run", "--topology", "topology.yaml", "--bench", "qkv_gemm",
+    ])
+    assert rc == 0
+
+
+def test_cmd_run_verify_data_enables_engine():
+    """--verify-data runs full pipeline with enable_data=True and DataExecutor."""
+    rc = cli_main.main([
+        "run", "--topology", "topology.yaml", "--bench", "qkv_gemm",
+        "--device", "sip:0", "--verify-data",
+    ])
+    assert rc == 0
+
+
+def test_cmd_run_without_verify_data_no_op_log():
+    """Without --verify-data, engine runs in timing-only mode (no op_log)."""
+    rc = cli_main.main([
+        "run", "--topology", "topology.yaml", "--bench", "qkv_gemm",
+        "--device", "sip:0",
+    ])
+    assert rc == 0