[WP32] N2K state core and emitters

[mbuckton]

Scope

Review and deterministic JUnit coverage for io.mapsmessaging.state.n2k and io.mapsmessaging.state.n2k.handler.

Tests added

• N2K session lifecycle, cleanup, idempotency and post-stop delivery
• Twin position/motion validity, partial updates and stale-event rejection
• AIS report prerequisites, report types, scheduling, material-change thresholds and signatures
• Heading/course wrap-around and geodetic boundary calculations
• Drone monitor emission isolation and cleanup

Confirmed bugs fixed

• Repeated session start/stop and post-stop events were not guarded
• Startup/shutdown failures could skip protocol cleanup
• Stale navigation or motion events could overwrite newer twin state
• Null-to-null motion values were treated as material changes
• Near-antipodal distance calculations could return NaN
• PGN 129040 bypassed the half-interval material-change throttle used by PGN 129039
• Monitor shutdown retained per-drone emission state

Verification

A work-package-specific GitHub Actions run executes targeted tests, the complete Maven test suite and assigned-package JaCoCo extraction. Final commands and coverage will be recorded in docs/review/WP32-README.md.

Remaining risks

SocketCAN, real CAN interfaces and live N2K traffic are explicitly excluded. The parser/protocol boundary is exercised with test doubles.

[coderabbitai]

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch review/state-n2k-core

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