Add protocol-certification M9 L3 channel certifier (2.71.0).

L3 CHANNEL structure for timing budget, insertion loss, return loss,
crosstalk, and complete channel. Numeric PASS/FAIL only from existing
channel FACT; otherwise a visible skip. No OpenEMS, no invented S-parameters,
no M6 packs.

tests/pcb/test_protocol_l2_m4.py

@@ -204,8 +204,8 @@ def test_axi_internal_l2_not_applicable():
     assert rows
     assert all(r.result == "NOT_APPLICABLE" for r in rows)
     sec, findings = protocol_exam(_axi_graph())
-    assert sec.max_level_reached == "L2"
-    assert sec.macrophase == "M8"
+    assert sec.max_level_reached == "L3"
+    assert sec.macrophase == "M9"
     assert all(f.status != "ERROR" for f in findings)
     blob = json.dumps([r.model_dump() for r in rows])
     assert "L0/L1 are not electrical" in blob
@@ -253,7 +253,7 @@ def test_l2_does_not_run_l3_or_geometry():
 
 def test_protocol_exam_attaches_l2_checks():
     sec, _ = protocol_exam(_usb_connected())
-    assert sec.max_level_reached == "L2"
+    assert sec.max_level_reached == "L3"
     row = sec.recognized_instances[0]
     assert row.get("l2_checks")
     assert all(c.get("level") == "L2" for c in row["l2_checks"])