Port GOOSE PDU and Ethernet frame codecs

[masarray]

Scope

Phase 1B adds the deterministic offline GOOSE wire layer:

• GOOSE PDU model and BER codec from gocbRef through allData.
• numDatSetEntries validation against decoded MMS values.
• Complete Ethernet/VLAN/process-bus frame encode/decode support.
• C#-derived byte-for-byte PDU and Ethernet golden vectors.
• Malformed UTC time, outer-tag, dataset-count, and EtherType rejection tests.
• Migration checklist and consolidated CMake warning configuration.

Validation

The branch was rebuilt as one clean Phase 1B commit on top of merged main; GitHub Actions will validate GCC, Clang, and Windows MSVC again before merge.

Safety boundary

Offline wire codecs only. No network-interface access, active publishing, MMS writes, or IED control.

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