docs: fill payload request-response TODOs from current handlers

[robekl]

Summary

Targeted completion of TODO/omission sections in docs/payloads.md using current request/response handlers.

Changes

• Replaced TODO content for request/response sections with explicit field-level payload descriptions for:
  • telemetry requests/responses
  • sensor avg/min/max requests/responses
  • ACL list requests/responses
  • repeater neighbors requests/responses
  • repeater owner-info response.
• Clarified keepalive request description (active flow, not deprecated in current handler usage).
• Added response tag/content description using echoed sender_timestamp.
• Fixed typo: Get Neighors -> Get Neighbors.
• Removed inaccurate "current free queue length" item from status bullets.

Implementation References

• examples/simple_repeater/MyMesh.cpp
  • REQ_TYPE_GET_STATUS
  • REQ_TYPE_GET_TELEMETRY_DATA
  • REQ_TYPE_GET_ACCESS_LIST
  • REQ_TYPE_GET_NEIGHBOURS
  • REQ_TYPE_GET_OWNER_INFO
  • MyMesh::handleRequest
• examples/simple_room_server/MyMesh.cpp
  • REQ_TYPE_GET_STATUS
  • REQ_TYPE_GET_TELEMETRY_DATA
  • REQ_TYPE_GET_ACCESS_LIST
  • MyMesh::handleRequest
  • REQ_TYPE_KEEP_ALIVE handling in onPeerDataRecv
• examples/simple_sensor/SensorMesh.cpp
  • REQ_TYPE_GET_TELEMETRY_DATA
  • REQ_TYPE_GET_AVG_MIN_MAX
  • REQ_TYPE_GET_ACCESS_LIST
  • SensorMesh::handleRequest
• src/helpers/BaseChatMesh.cpp
  • request/response timestamp/tag pattern in peer request flow