special case no sent/received message in network health check

[ceyonur]

Why this should be merged

lastSend and lastReceived time values default to 0, which would show errors in health check like:

{
  "network": {
    "message": {
      "connectedPeers": 0,
      "sendFailRate": 0,
      "timeSinceLastMsgReceived": "466123h20m46.862257771s",
      "timeSinceLastMsgSent": "466123h20m46.862257771s"
    },
    "error": "network layer is unhealthy reason: not connected to a minimum of 1 peer(s) only 0, no messages from network received in 466123h20m46.862257771s > 1m0s, no messages from network sent in 466123h20m46.862257771s > 1m0s",
    "timestamp": "2023-03-05T19:20:46.862278635Z",
    "duration": 56961,
    "contiguousFailures": 1,
    "timeOfFirstFailure": "2023-03-05T19:20:46.862278635Z"
  }
}

466123h20m46.862257771s > 1m0s seems a bit off.

This PR handles this case, so that we won't show time.Now in timeSinceLastMsgReceived/Sent and show them like:

"network": {
    "message": {
        "connectedPeers": 0,
        "sendFailRate": 0
    },
    "error": "network layer is unhealthy reason: not connected to a minimum of 1 peer(s) only 0, no messages received from network, no messages sent to network",
    "timestamp": "2023-03-29T14:04:08.258799+03:00",
    "duration": 104750,
    "contiguousFailures": 1,
    "timeOfFirstFailure": "2023-03-29T14:04:08.258799+03:00"
},

How this works

Special cases the case where last send/received = 0 in network health function. It also puts storing/reading these values into functions.

How this was tested

Locally tested

[StephenButtolph]

Some small readability suggestions