Add tests for count string deserialization (fixes #35)

The API returns the count field as a JSON string instead of a number,
causing JsonException on Lookup(), BulkLookup(), and Lookup(culture).
Added test cases for both string and numeric count values, and updated
the test fixture to include count as a string matching real API behavior.

https://claude.ai/code/session_01V2uek6e28i6ARom7qVt1Mz

Author: claude

test/Unit/IPData.Tests/DataSources/TestData/IPLookupResult.json

@@ -67,5 +67,6 @@
     "is_bogon": false,
     "blocklists": []
   },
-  "status": 200
+  "status": 200,
+  "count": "213586"
 }

test/Unit/IPData.Tests/Http/Serializer/JsonSerializerTests.cs

@@ -21,6 +21,32 @@ public void Deserialize_WhenCalled_ReturnedIPLookupResult(string json)
             actual.Should().NotBeNull();
         }
 
+        [Fact]
+        public void Deserialize_CountAsString_ParsedCorrectly()
+        {
+            // Arrange - API returns count as a string (issue #35)
+            var json = "{\"count\": \"213586\"}";
+
+            // Act
+            var actual = _sut.Deserialize<IPLookupResult>(json);
+
+            // Assert
+            actual.Count.Should().Be(213586);
+        }
+
+        [Fact]
+        public void Deserialize_CountAsNumber_ParsedCorrectly()
+        {
+            // Arrange
+            var json = "{\"count\": 213586}";
+
+            // Act
+            var actual = _sut.Deserialize<IPLookupResult>(json);
+
+            // Assert
+            actual.Count.Should().Be(213586);
+        }
+
         [Theory, AutoMoqData]
         public void SerializeIPLookupResult_WhenCalled_ReturnedString(IPLookupResult ipInfo)
         {