SV core: unify generic analysis and measurement ownership

[masarray]

Purpose

Move reusable Sampled Values analysis that had diverged inside the ARSVIN application repository into ARIEC61850, which is the single source of truth for protocol and engineering behavior.

Audit result

The following reusable components existed in ARSVIN's embedded engine but were absent from ARIEC61850/main:

• conservative engineering scaling with no unbound unit inference
• profile-neutral smpCnt transition tracking
• evidence-driven timebase resolution without a hidden 50/60 Hz assumption
• explicit CT/VT ratio and primary/secondary-domain conversion
• semantic Sampled Values quality decoding
• versioned stream measurement-context JSON
• generic ASDU inspection
• generic seqOfData word inspection with preserved trailing bytes

Implemented

• adds the eight public engine components under src/AR.Iec61850/SampledValues
• keeps all logic vendor-neutral; device identity never selects parsing, mapping, scaling, quality, timebase, or health
• adds deterministic tests covering generic payload/ASDU inspection, scaling gates, timebase, counter continuity, quality, ratios, and context serialization
• documents the ownership boundary between ARIEC61850 and derived applications

Integration

Companion ARSVIN draft PR masarray/arsvin#51 references this repository as a sibling project and stops compiling its embedded ARSVIN.Engine copy. The two PRs are intentionally left unmerged for paired local testing.

Validation at head 7923a28

• source hygiene, provenance, wording, and current-license checks: passed
• full solution restore: passed
• full solution build: passed
• deterministic test suite: passed
• .NET CI run 207: passed

This validates software integration and deterministic fixtures only. Real MU/SCL/PCAP/known-injection interoperability evidence remains a separate test gate.

Safety boundary

This is engineering software and deterministic regression evidence, not formal IEC 61850 conformance certification or calibrated measurement validation.