Fix JsonException when API returns count as string

The IPData API returns the `count` field as a JSON string, but the
model expected System.Int32. Add IntJsonConverter to handle both
string and number JSON tokens for the Count property.

https://claude.ai/code/session_01V2uek6e28i6ARom7qVt1Mz

Author: claude

src/IPData/Http/Serializer/IntJsonConverter.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace IPData.Http.Serializer
+{
+    internal class IntJsonConverter : JsonConverter<int>
+    {
+        public override int Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        {
+            if (reader.TokenType == JsonTokenType.String)
+            {
+                var stringValue = reader.GetString();
+                if (int.TryParse(stringValue, out var value))
+                {
+                    return value;
+                }
+
+                throw new JsonException($"Unable to convert \"{stringValue}\" to System.Int32.");
+            }
+
+            return reader.GetInt32();
+        }
+
+        public override void Write(Utf8JsonWriter writer, int value, JsonSerializerOptions options)
+        {
+            writer.WriteNumberValue(value);
+        }
+    }
+}

src/IPData/Models/IPLookupResult.cs

@@ -4,6 +4,7 @@
 using System.Linq.Expressions;
 using System.Text.Json.Serialization;
 using IPData.Helpers.Extensions;
+using IPData.Http.Serializer;
 
 namespace IPData.Models
 {
@@ -88,6 +89,7 @@ public class IPLookupResult
         public int? Status { get; set; }
 
         [JsonPropertyName("count")]
+        [JsonConverter(typeof(IntJsonConverter))]
         public int Count { get; set; }
 
         internal static string FieldName(Expression<Func<IPLookupResult, object>> expression)