Add probe CLI improvements, D2H read, UCIe/HBM tuning, BW sweep

- Probe CLI: restructured output (tables first, routes below), per-hop
  timestamps, split cross-cube into best/worst cases, D2H read section
- UCIe overhead: 1ns -> 8ns per port (16ns per crossing) to fix
  cross-cube-best < cross-half latency inversion
- HBM efficiency: added efficiency=0.8 factor to hbm_ctrl, reducing
  effective BW from 256 to 204.8 GB/s
- Multi-size BW sweep: saturation tables (4KB-1MB) for all probe cases
- Probe default data size: 4KB -> 32KB for more realistic measurements
- IOChiplet NOC + D2H topology and tests
- NOC mesh, xbar, BW occupancy components and tests
- Cube mesh visualization diagram

278 tests pass.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_engine.py

@@ -327,11 +327,13 @@ def test_formula_latency_lower_bound():
     assert formula > 0, "formula must be > 0"
 
 
-def test_formula_latency_exact_no_contention():
-    """With no contention, formula should approximate actual for PE DMA.
+def test_formula_latency_lower_bound_no_contention():
+    """With no contention, formula is a lower bound for PE DMA.
 
-    PE DMA is single-request with no fan-out or aggregation,
-    so formula ≈ actual (within small tolerance for SimPy scheduling).
+    PE DMA routes through NOC, which applies internal mesh traversal
+    latency (XY routing based on physical positions) not captured by the
+    formula (NOC edges have distance_mm=0 since NOC is distributed).
+    Formula <= actual is the invariant.
     """
     from kernbench.runtime_api.kernel import PeDmaMsg
     from kernbench.policy.address.phyaddr import PhysAddr as PA
@@ -360,10 +362,11 @@ def test_formula_latency_exact_no_contention():
     _, trace = engine.get_completion(h)
     actual = trace["total_ns"]
 
-    # No contention: formula should equal actual
-    assert abs(formula - actual) < 0.01, (
-        f"formula ({formula:.4f}) ≈ actual ({actual:.4f}) expected with no contention"
+    # Formula is a lower bound; NOC internal traversal adds latency
+    assert formula <= actual + 0.01, (
+        f"formula ({formula:.4f}) must be <= actual ({actual:.4f})"
     )
+    assert actual > 0
 
 
 # ── 10. remote cube access succeeds with higher latency ────────────