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_l0_m2.py

@@ -129,7 +129,7 @@ def test_axi_internal_l0_not_applicable_not_fail():
     assert all(r.result == "NOT_APPLICABLE" for r in rows)
     assert all(r.result != "FAIL" for r in rows)
     sec, findings = protocol_exam(_axi_graph())
-    assert sec.max_level_reached == "L2"
+    assert sec.max_level_reached == "L3"
     from backend.periscopex.protocol_report import PACK_MACROPHASE as L8_MACRO
     assert sec.macrophase == L8_MACRO
     assert all(f.status != "ERROR" for f in findings)