Deserialization of metrics from OTLP output broken

[scottgerring]

Identified during #2432. Given this code:

    async fn test_roundtrip_example_data() -> Result<()> {
        let metrics_in = include_str!("../expected/metrics/test_u64_counter_meter.json");
        let metrics: MetricsData = serde_json::from_str(metrics_in)?;
        let metrics_out = serde_json::to_string(&metrics)?;

        println!("{:}", metrics_out);

        let metrics_in_json: Value = serde_json::from_str(metrics_in)?;
        let metrics_out_json: Value = serde_json::from_str(&metrics_out)?;

        assert_eq!(metrics_in_json, metrics_out_json);

        Ok(())
    }

And some sample data:

{
  "resourceMetrics": [
    {
      "resource": {
        "attributes": [
          {
            "key": "service.name",
            "value": {
              "stringValue": "metrics-integration-test"
            }
          }
        ]
      },
      "scopeMetrics": [
        {
          "scope": {
            "name": "test_u64_counter_meter"
          },
          "metrics": [
            {
              "name": "counter_u64",
              "sum": {
                "dataPoints": [
                  {
                    "attributes": [
                      {
                        "key": "mykey1",
                        "value": {
                          "stringValue": "myvalue1"
                        }
                      },
                      {
                        "key": "mykey2",
                        "value": {
                          "stringValue": "myvalue2"
                        }
                      }
                    ],
                    "startTimeUnixNano": "1734255506254812000",
                    "timeUnixNano": "1734255533415552000",
                    "asInt": "10"
                  }
                ],
                "aggregationTemporality": 2,
                "isMonotonic": true
              }
            }
          ]
        }
      ]
    }
  ]
}

The assertion fails:

  left: Object {"resourceMetrics": Array [Object {"resource": Object {"attributes": Array [Object {"key": String("service.name"), "value": Object {"stringValue": String("metrics-integration-test")}}]}, "scopeMetrics": Array [Object {"metrics": Array [Object {"name": String("counter_u64"), "sum": Object {"aggregationTemporality": Number(2), "dataPoints": Array [Object {"asInt": String("10"), "attributes": Array [Object {"key": String("mykey1"), "value": Object {"stringValue": String("myvalue1")}}, Object {"key": String("mykey2"), "value": Object {"stringValue": String("myvalue2")}}], "startTimeUnixNano": String("1734255506254812000"), "timeUnixNano": String("1734255533415552000")}], "isMonotonic": Bool(true)}}], "scope": Object {"name": String("test_u64_counter_meter")}}]}]}
 right: Object {"resourceMetrics": Array [Object {"resource": Object {"attributes": Array [Object {"key": String("service.name"), "value": Object {"stringValue": String("metrics-integration-test")}}], "droppedAttributesCount": Number(0)}, "schemaUrl": String(""), "scopeMetrics": Array [Object {"metrics": Array [Object {"description": String(""), "metadata": Array [], "name": String("counter_u64"), "sum": Object {"aggregationTemporality": Number(2), "dataPoints": Array [Object {"attributes": Array [Object {"key": String("mykey1"), "value": Object {"stringValue": String("myvalue1")}}, Object {"key": String("mykey2"), "value": Object {"stringValue": String("myvalue2")}}], "exemplars": Array [], "flags": Number(0), "startTimeUnixNano": String("1734255506254812000"), "timeUnixNano": String("1734255533415552000")}], "isMonotonic": Bool(true)}, "unit": String("")}], "schemaUrl": String(""), "scope": Object {"attributes": Array [], "droppedAttributesCount": Number(0), "name": String("test_u64_counter_meter"), "version": String("")}}]}]}

There's a bunch of things that are unimportant, but the asInt in dataPoints goes missing, and this is the metric value itself. Raising a separate issue as this feels like it could be a serde-and-protobuf-can-of-worms.