Harden MSI UDP correlation and completion

[stevenboyd78]

Summary

• add direct regression coverage proving an exact one-shot MSI UDP expectation survives unrelated bare ScannerInfo, GLT, and AST XML roots until matching MSI XML arrives
• add transport-level regression coverage proving successful MSI completion after an automatic sequence-gap retry removes stale one-shot retry authority, so later stray MSI fragment gaps cannot resend the completed request
• keep this sixth Milestone 24.8 slice production-code neutral and update the roadmap/research history accordingly

Validation

• ruff check .
• mypy src/sds200 — 137 source files
• python -m pytest — 3621 passed
• python scripts/check_docs.py — 47 Markdown files
• package wheel/sdist build
• twine check dist/*
• exact feature-SHA push CI run and all five check runs completed successfully

Evidence boundary

This slice adds deterministic fake-datagram regression coverage only. It does not add production protocol behavior or claim physical scanner/firmware applicability. MSV/MSB [RSV] serialization, unindexed MNU, fallback MSI, menu lifecycle/state ownership, renderer behavior, and physical validation remain deferred.