Add functions to catch timeseries schema changes

- Move schema types from the `oximeter-db` crate to `oximeter` proper
- Add a `SchemaSet` for storing a unique set of timeseries schema, and
  comparing against a set deserialized from file. This works like
  expectorate, with a few tweaks, and allows developers to catch any
  changes. If we want to relax this to catching _compatible_ changes,
  for some definition of that, we can do that pretty easily.

oximeter/collector/src/self_stats.rs

@@ -154,8 +154,15 @@ impl CollectionTaskStats {
 
 #[cfg(test)]
 mod tests {
+    use super::Collections;
+    use super::Cumulative;
+    use super::FailedCollections;
     use super::FailureReason;
+    use super::OximeterCollector;
     use super::StatusCode;
+    use oximeter::schema::SchemaSet;
+    use std::net::IpAddr;
+    use std::net::Ipv6Addr;
 
     #[test]
     fn test_failure_reason_serialization() {
@@ -168,4 +175,50 @@ mod tests {
             assert_eq!(variant.to_string(), *as_str);
         }
     }
+
+    const fn collector() -> OximeterCollector {
+        OximeterCollector {
+            collector_id: uuid::uuid!("cfebaa5f-3ba9-4bb5-9145-648d287df78a"),
+            collector_ip: IpAddr::V6(Ipv6Addr::LOCALHOST),
+            collector_port: 12345,
+        }
+    }
+
+    fn collections() -> Collections {
+        Collections {
+            producer_id: uuid::uuid!("718452ab-7cca-42f6-b8b1-1aaaa1b09104"),
+            producer_ip: IpAddr::V6(Ipv6Addr::LOCALHOST),
+            producer_port: 12345,
+            base_route: String::from("/"),
+            datum: Cumulative::new(0),
+        }
+    }
+
+    fn failed_collections() -> FailedCollections {
+        FailedCollections {
+            producer_id: uuid::uuid!("718452ab-7cca-42f6-b8b1-1aaaa1b09104"),
+            producer_ip: IpAddr::V6(Ipv6Addr::LOCALHOST),
+            producer_port: 12345,
+            base_route: String::from("/"),
+            reason: FailureReason::Unreachable.to_string(),
+            datum: Cumulative::new(0),
+        }
+    }
+
+    // Check that the self-stat timeseries schema have not changed.
+    #[test]
+    fn test_no_schema_changes() {
+        let collector = collector();
+        let collections = collections();
+        let failed = failed_collections();
+        let mut set = SchemaSet::default();
+        assert!(set.insert_checked(&collector, &collections).is_none());
+        assert!(set.insert_checked(&collector, &failed).is_none());
+
+        const PATH: &'static str = concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/tests/output/self-stat-schema.json"
+        );
+        set.assert_contents(PATH);
+    }
 }

oximeter/collector/tests/output/self-stat-schema.json

@@ -0,0 +1,91 @@
+{
+  "oximeter_collector:collections": {
+    "timeseries_name": "oximeter_collector:collections",
+    "field_schema": [
+      {
+        "name": "base_route",
+        "field_type": "string",
+        "source": "metric"
+      },
+      {
+        "name": "collector_id",
+        "field_type": "uuid",
+        "source": "target"
+      },
+      {
+        "name": "collector_ip",
+        "field_type": "ip_addr",
+        "source": "target"
+      },
+      {
+        "name": "collector_port",
+        "field_type": "u16",
+        "source": "target"
+      },
+      {
+        "name": "producer_id",
+        "field_type": "uuid",
+        "source": "metric"
+      },
+      {
+        "name": "producer_ip",
+        "field_type": "ip_addr",
+        "source": "metric"
+      },
+      {
+        "name": "producer_port",
+        "field_type": "u16",
+        "source": "metric"
+      }
+    ],
+    "datum_type": "cumulative_u64",
+    "created": "2023-11-30T23:10:15.013761925Z"
+  },
+  "oximeter_collector:failed_collections": {
+    "timeseries_name": "oximeter_collector:failed_collections",
+    "field_schema": [
+      {
+        "name": "base_route",
+        "field_type": "string",
+        "source": "metric"
+      },
+      {
+        "name": "collector_id",
+        "field_type": "uuid",
+        "source": "target"
+      },
+      {
+        "name": "collector_ip",
+        "field_type": "ip_addr",
+        "source": "target"
+      },
+      {
+        "name": "collector_port",
+        "field_type": "u16",
+        "source": "target"
+      },
+      {
+        "name": "producer_id",
+        "field_type": "uuid",
+        "source": "metric"
+      },
+      {
+        "name": "producer_ip",
+        "field_type": "ip_addr",
+        "source": "metric"
+      },
+      {
+        "name": "producer_port",
+        "field_type": "u16",
+        "source": "metric"
+      },
+      {
+        "name": "reason",
+        "field_type": "string",
+        "source": "metric"
+      }
+    ],
+    "datum_type": "cumulative_u64",
+    "created": "2023-11-30T23:10:15.014347842Z"
+  }
+}

oximeter/db/src/client.rs

@@ -710,7 +710,7 @@ impl Client {
         &self,
         sample: &Sample,
     ) -> Result<Option<(TimeseriesName, String)>, Error> {
-        let sample_schema = model::schema_for(sample);
+        let sample_schema = TimeseriesSchema::from(sample);
         let name = sample_schema.timeseries_name.clone();
         let mut schema = self.schema.lock().await;
 
@@ -1871,7 +1871,7 @@ mod tests {
         client.insert_samples(&[sample.clone()]).await.unwrap();
 
         // The internal map should now contain both the new timeseries schema
-        let actual_schema = model::schema_for(&sample);
+        let actual_schema = TimeseriesSchema::from(&sample);
         let timeseries_name =
             TimeseriesName::try_from(sample.timeseries_name.as_str()).unwrap();
         let expected_schema = client