fix(server): harden edge cases with regression coverage

[mbuckton]

Summary

This branch started as test-flake cleanup and was expanded into a focused coverage pass. The majority of the diff is test/support code, with small production fixes only where regression tests demonstrated incorrect behavior.

Test and coverage work

• Stabilize periodic runner and high-fanout ordering tests.
• Gate tests that require external CAN/satellite dependencies.
• Add happy, sad, and Murphy coverage for device configuration, routing metrics, CIDR matching, cache behavior, battery duration, geographic utilities, endpoint DTO helpers, MQTT Will configuration, and internal message transformation.
• Archive merged JaCoCo XML from the sharded Jenkins run.

Production fixes proven by tests

• Parse hexadecimal I2C addresses correctly.
• Correct Serial, OneWire, and SPI configuration update/round-trip behavior.
• Implement the previously stubbed SerialDeviceConfig serialization/update contract.
• Preserve MQTT Will payload encoding during updates.
• Handle endpoints before protocol detection completes.
• Fix route metric sampling and millisecond timestamps.
• Reject invalid CIDR prefix lengths.
• Preserve serialized message metadata/state through Message JSON transformation.
• Wait for HA lock worker threads to stop during close.
• Process the exact SimpleStats interval boundary.
• Store CoAP publishes before sending the acknowledgement.
• Preserve NATS publish ordering.
• Remove unused FqnTree.

Review notes

Against the current development branch, the diff is predominantly tests/support:

• 24 test/support files, about 1,436 added lines.
• 16 runtime files, about 173 added lines.

The NATS publish-ordering change is the most significant runtime behavior change. It waits for asynchronous destination resolution before storing the message, providing ordering/backpressure rather than dispatching stores from completion callbacks.

Verification

An earlier Jenkins run on this branch completed with 0 failures and increased coverage by approximately 0.5 percentage points.

The current head contains an additional coverage/fix batch after that run, so a fresh Jenkins run is required before merge.

The branch is also currently behind development and should be updated/revalidated before merge.

[coderabbitai]

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