Harden MAVLink transport and state lifecycle

[mbuckton]

Summary

This change hardens the existing MAVLink implementation without changing the protocol architecture used elsewhere in MapsMessaging.

Changes

• prevent logical UDP facade sessions from closing the shared physical UDP endpoint
• process packets received from configured forwarders through the normal MAVLink pipeline without forwarding loops
• contain failed session creation and always restore selector read registration
• retain and cancel scheduled MAVLink heartbeat tasks
• support serial endpoints without parsing their device name as a network socket
• separate serial input and output scratch buffers
• correct MAVLink v1 serial framing to read four header bytes after magic and payload length
• track MAVLink sequence state independently per component
• support JSON list-backed numeric arrays in typed MAVLink packets
• clean up twin observers and partially started state subscribers
• preserve model-provided detection contact identifiers
• contain malformed telemetry in the state subscriber

Tests

• deterministic concurrent serial input/output regression test
• MAVLink v1 serial frame-length and byte-preservation coverage
• JSON numeric-list to integer-array conversion coverage
• invalid JSON array element coverage

Scope

The MAVLink schema library remains responsible for MAVLink packet formats and encoding. These changes are limited to transport flow, session/state lifecycle, error containment, and the server-side handoff around that schema layer.

[coderabbitai]

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