feat: add CoreNetwork API coverage

[jmcte]

Summary

• add CoreNetwork wrapper coverage for DSM network APIs
• include authentication, IPv6, MAC clone, OVS, PPPoE relay, static routes, traffic control, UPnP, and WOL helpers
• add focused unit tests for request construction

Tests

• python -m pytest tests/test_core_network.py

[jmcte]

I proactively updated the tests here to match the same request-contract approach from the CoreExternalDevice PR. These now assert API namespace, path, version, DSM method, request parameters, optional parameter omission, and boolean conversion for representative wrapper methods instead of only checking that request_data was called.