Relocate shared engine source and expand protocol tests

[masarray]

Purpose

Complete the remaining P2 architecture and coverage work by moving the shared IEC 61850 engine source physically under src/ARSVIN.Engine, expanding deterministic regression tests, and raising enforced coverage baselines.

Completed changes

Physical shared-engine ownership

• Moved 180 tracked engine source files from src/ARSVIN/Engine into src/ARSVIN.Engine using git mv.
• Removed the external wildcard compile-link from ARSVIN.Engine.csproj.
• Removed the Publisher-side Compile Remove workaround.
• Publisher, Subscriber, and Tests continue to reference one compiled ARSVIN.Engine assembly.
• Removed the temporary inventory/relocation workflow before review.

Expanded deterministic regression tests

• Increased the test suite from 26 to 54 tests.
• Added SCL stream, address, report-control, warning, and file-loading tests.
• Added COMTRADE ASCII parsing, scaling, timestamp fallback, indexing, and unsupported-format tests.
• Added PCAP read/write round-trip and malformed-input tests.
• Added MMS data codec and object-reference tests.
• Added diagnostics HexDump tests.
• Added Sampled Values publisher-session counter, batching, API-guard, and wrap tests.

Protocol fix discovered by the tests

• Multi-ASDU Publisher sessions now apply the configured smpCnt wrap to every ASDU within the frame.
• A 4,000-sample wrap now emits 3998, 3999, 0, 1 rather than 3998, 3999, 4000, 4001.

Raised coverage gates

• Whole-engine coverage: 1,691 of 15,742 lines, 10.74%.
• Whole-engine regression floor raised to 10.5%.
• Protocol-core coverage: 1,007 of 1,550 lines, 64.97%.
• Protocol-core regression floor raised to 60%.
• README, build guidance, repository structure, and changelog now match the relocated source and measured baselines.

Validation completed

• Locked dependency restore: success.
• Public-site generation and recursive validation: success.
• Publisher warning-free build: success.
• Subscriber warning-free build: success.
• 54 tests: success.
• Whole-engine 10.5% coverage gate: success.
• Protocol-core 60% coverage gate: success.
• Publisher and Subscriber vulnerability reports: success.
• Full-solution CodeQL: success.
• Portable Publisher and Subscriber publish: success.
• Inno Setup installer compilation: success.
• CycloneDX SBOM validation: success.
• Silent installer and uninstaller smoke tests: success.
• SHA-256 checksum generation: success.
• Public release job on the PR: correctly skipped.

Validated private artifact: ARSVIN-0.0.0-pr.72-windows-x64, digest sha256:62819271b6089a620050f9d54ae780050091bceb373a2867b6b3a6106af2d832.

No public GitHub Release is created by this pull request.