Gate path updates to unknown, better-hop, or stale routes

[robekl]

Summary

This change replaces unconditional contact path overwrites with a simple acceptance gate so routing state is more stable under noisy/frequent path updates.

Problem

Current path handling effectively behaves like "last received path wins" for contact/client out_path.
That can cause route churn when equal-or-worse paths arrive after a good path.

What Changed

• Added PATH_STALE_SECS (default 60) in:
  • src/helpers/BaseChatMesh.cpp
  • examples/simple_sensor/SensorMesh.cpp
• Added a small helper:
  • pathHopCount(path_len) using lower 6 bits of path_len.
• Updated path update logic to accept a new path only when:
  • existing path is unknown, or
  • new path has fewer hops, or
  • existing path is stale.
• Added debug logs for rejected non-improving path updates.
• Left existing ACK/response extra payload behavior unchanged.

Behavior Impact

• Reduces path flapping.
• Preserves fast adoption of clearly better paths.
• Allows recovery from stale routes without introducing multi-path complexity.