fix(ocpp20): remediate 4 conformance findings from cross-audit

fix(ocpp20): remediate 4 conformance findings from cross-audit

- M04.FR.06: Narrow DeleteCertificate guard to V2GCertificateChain type
  only, allowing legitimate deletion of root certificates (CSMSRoot,
  ManufacturerRoot, MORootCert, V2GRoot)
- B09.FR.05: Use InvalidConfSlot reasonCode per errata 2025-09 when
  configurationSlot is not in NetworkConfigurationPriority list
- B09.FR.04/FR.31: Check AllowSecurityProfileDowngrade variable before
  rejecting downgrades — allow 3→2 when true, never allow to profile 1
  (errata 2025-09 §2.12)
- L01.FR.06: Wait for active transactions to end before commencing
  firmware installation via polling loop in lifecycle simulation