Add protocol-certification M4 L2 electrical certifier (2.68.0).

Z/termination/levels from datasheet, stackup, fab, or cited pack only. Never invented USB ohms. No L3/OpenEMS. L0/L1 are not electrical.

tests/pcb/test_protocol_l1_m3.py

@@ -165,8 +165,8 @@ def test_axi_internal_l1_not_applicable():
     assert all(r.result == "NOT_APPLICABLE" for r in rows)
     assert all(r.result != "FAIL" for r in rows)
     sec, exam_findings = protocol_exam(_axi_graph(), layout=LayoutGraph())
-    assert sec.max_level_reached == "L1"
-    assert sec.macrophase == "M3"
+    assert sec.max_level_reached == "L2"
+    assert sec.macrophase == "M4"
     assert all(f.status != "ERROR" for f in exam_findings)
     blob = json.dumps([r.model_dump() for r in rows])
     assert "electrical certification" not in blob.lower() or "not electrical" in blob.lower()
@@ -257,7 +257,7 @@ def test_l1_does_not_run_impedance():
 
 def test_protocol_exam_attaches_l1_checks():
     sec, _ = protocol_exam(_usb_connected(), layout=_usb_layout())
-    assert sec.max_level_reached == "L1"
+    assert sec.max_level_reached == "L2"
     assert sec.recognized_instances
     row = sec.recognized_instances[0]
     assert row.get("l1_checks")