fix(mavlink): harden twin state management

[mbuckton]

Scope

Consolidates the MAVLink twin/state fixes reviewed from:

• agent/mavlink-runtime-hardening
• feature/mavlink-transport-lifecycle-fixes
• review/state-mavlink-bootstrap

This branch starts from current development and contains no endpoint/network transport changes.

Required fixes retained

• decode Gson List<Number> values as MAVLink numeric arrays
• decode JSON number lists used for MAVLink fixed-width character arrays
• preserve DetectionEvent.contactId for DETECTED/UPDATED/LOST contact lifecycle
• return the canonical twin registered by TwinManager
• make updater/subscriber/observer close idempotent and ignore late updates
• clean up protocol and observer resources after start, subscribe, unsubscribe, or close failures
• defer readiness evaluation until listener-driven twin mutations finish
• prevent recursive readiness observer updates
• stamp valid battery packet freshness
• reject invalid coordinates, GPS sentinel values, and unusable battery measurements
• block stale power from command-ready state
• reset bootstrap request trackers after missing state recovery

MAVLink JSON arrays

MAVLink contains both numeric arrays (for example BATTERY_STATUS.voltages and voltages_ext) and fixed-width character arrays (for example status text and names). Gson deserializes those JSON arrays as lists, so both numeric and character-list decoding are retained.

Tests

Adds focused coverage for:

• packet numeric and character JSON lists, including malformed mixed lists
• contact ID add/lost lifecycle
• updater battery freshness, ordering, registration, close, and late messages
• subscriber start/stop failure cleanup and idempotence
• monitor lifecycle and recursion prevention
• readiness validity/freshness combinations
• bootstrap request retry/reset/timeout transitions
• source registry matching

Deliberately excluded

• formatting/import-only churn and review documentation
• broad runtime swallowing in the subscriber message handler; programming faults still propagate after logging
• all endpoint/network transport changes (separate PR)

Validation note

Focused Maven execution was attempted, but this environment cannot resolve repository.mapsmessaging.io or Maven Central. GitHub Actions is the authoritative test run for this draft.

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