fix(offchain): fixed timestamp in graphql

[gligneul]

The timestamp was intepreted in milliseconds, but it should be interpreted in seconds.
Also removes the chrono dependency because it is not necessary.

[gligneul]

Tested with examples and it fixes the issue:

{
  "data": {
    "inputs": {
      "edges": [
        {
          "node": {
            "timestamp": 1693868070
          }
        }
      ]
    }
  }
}