Calibrate 3 tests for ADR-0033 Phase 2c per-flit wire timing

- test_h2d_local_cube_cut_through: threshold 65 → 80ns. The cut-through
  invariant (vs store-and-forward ~160ns at 4KB through UCIe) is what
  the test guards; the previous 65ns ceiling was too tight against the
  small per-flit overhead now charged at wire.
- test_engine_override_is_scoped_to_impl: ZeroRouter inherits
  TransitComponent (was ComponentBase). Inheriting bare ComponentBase
  reverts the override path to non-flit-aware reassembly, making
  override slower than default and inverting the test. The test's
  intent is overhead=0 vs overhead=2, not flit-awareness.
- test_intra_sip_critical_path_at_96k_below_threshold: threshold
  20.5 → 30 µs. Allreduce absolute timing is sensitive to model
  fidelity; the algorithmic invariant (8-hop center root < 12-hop
  corner root) is preserved within the new envelope.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_probe.py

@@ -115,15 +115,17 @@ def test_single_pe_write_deterministic():
 
 
 def test_h2d_local_cube_cut_through():
-    """H2D to local cube with cut-through should be < 50ns for 4096B.
+    """H2D to local cube with cut-through should be well below store-and-forward.
 
     Full command path: pcie_ep → io_cpu → ucie → noc → m_cpu
-    DMA: m_cpu → router mesh → hbm_ctrl (drain once at terminal)
-    Plus response path back.
-    With store-and-forward each hop would serialize; cut-through keeps it low.
+    DMA: m_cpu → router mesh → hbm_ctrl (drain once at bottleneck link)
+    Plus response path back. With store-and-forward each hop would serialize
+    nbytes through it (~5 × drain = 160ns for 4KB through UCIe 128 GB/s);
+    cut-through (ADR-0033 Phase 2c wormhole) keeps total dominated by the
+    single bottleneck transit.
     """
     lat = _h2d_latency(dst_cube=0, dst_pe=0)
-    assert lat < 65.0, f"Local H2D {lat:.2f}ns; cut-through expects < 65ns"
+    assert lat < 80.0, f"Local H2D {lat:.2f}ns; cut-through expects < 80ns (SAW would be > 160ns)"
 
 
 def test_h2d_remote_cube_cut_through():