fix: dapper doesn't play nice with List<T>

Catalogger.Backend/Database/Dapper/DatabasePool.cs

@@ -14,6 +14,9 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 using System.Data;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Catalogger.Backend.Database.Models;
 using Dapper;
 using NodaTime;
 using Npgsql;
@@ -113,6 +116,7 @@ public class DatabasePool
         SqlMapper.AddTypeHandler(new UlongArrayHandler());
 
         SqlMapper.AddTypeHandler(new PassthroughTypeHandler<Instant>());
+        SqlMapper.AddTypeHandler(new JsonTypeHandler<Guild.ChannelConfig>());
     }
 
     // Copied from PluralKit:
@@ -144,6 +148,21 @@ public class DatabasePool
         public override ulong[] Parse(object value) =>
             Array.ConvertAll((long[])value, i => (ulong)i);
     }
+
+    public class JsonTypeHandler<T> : SqlMapper.TypeHandler<T>
+    {
+        public override T Parse(object value)
+        {
+            string json = (string)value;
+            return JsonSerializer.Deserialize<T>(json)
+                ?? throw new CataloggerError("JsonTypeHandler<T> returned null");
+        }
+
+        public override void SetValue(IDbDataParameter parameter, T? value)
+        {
+            parameter.Value = JsonSerializer.Serialize(value);
+        }
+    }
 }
 
 public static class ServiceCollectionDatabaseExtensions