Improve change tracking performance

|          Method |     Mean |     Error |    StdDev | Ratio |   Gen0 | Allocated | Alloc Ratio |
|---------------- |---------:|----------:|----------:|------:|-------:|----------:|------------:|
|    TrackChanges | 3.741 us | 0.0122 us | 0.0114 us |  1.00 | 0.0229 |   6.41 KB |        1.00 |
| NewTrackChanges | 1.359 us | 0.0070 us | 0.0066 us |  0.36 | 0.0095 |   2.62 KB |        0.41 |

using BenchmarkDotNet.Attributes;
using JsonApiDotNetCore.Configuration;
using JsonApiDotNetCore.Middleware;
using JsonApiDotNetCore.Resources;
using JsonApiDotNetCore.Resources.Annotations;
using Microsoft.Extensions.Logging.Abstractions;

namespace Benchmarks.ChangeTracking;

// ReSharper disable once ClassCanBeSealed.Global
[MarkdownExporter]
[MemoryDiagnoser]
public class ChangeTrackerBenchmarks
{
    private readonly JsonApiRequest _request;
    private readonly TargetedFields _targetedFields;

    public ChangeTrackerBenchmarks()
    {
        IJsonApiOptions options = new JsonApiOptions();
        IResourceGraph resourceGraph = new ResourceGraphBuilder(options, NullLoggerFactory.Instance).Add<ExampleResource, long>().Build();
        ResourceType resourceType = resourceGraph.GetResourceType<ExampleResource>();

        _request = new JsonApiRequest
        {
            PrimaryResourceType = resourceType,
            IsCollection = true
        };

        _targetedFields = new TargetedFields();

        foreach (AttrAttribute attribute in resourceType.Attributes)
        {
            _targetedFields.Attributes.Add(attribute);
        }
    }

    [Benchmark(Baseline = true)]
    public void TrackChanges()
    {
        var changeTracker = new ResourceChangeTracker<ExampleResource>(_request, _targetedFields);

        var resource = new ExampleResource
        {
            Id = 1,
            Attr1 = "some",
            Attr2 = "more",
            Attr3 = "other",
            Attr4 = false,
            Attr5 = 123,
            Attr6 = default,
            Attr7 = default,
            Attr8 = default,
            Attr9 = DayOfWeek.Sunday
        };

        changeTracker.SetInitiallyStoredAttributeValues(resource);

        resource = new ExampleResource
        {
            Id = 1,
            Attr1 = "new",
            Attr2 = "change",
            Attr3 = "this",
            Attr4 = true,
            Attr5 = 456,
            Attr6 = default,
            Attr7 = default,
            Attr8 = default,
            Attr9 = DayOfWeek.Saturday
        };

        changeTracker.SetFinallyStoredAttributeValues(resource);

        changeTracker.HasImplicitChanges();
    }

    [Benchmark]
    public void NewTrackChanges()
    {
        var changeTracker = new NewResourceChangeTracker<ExampleResource>(_request, _targetedFields);

        var resource = new ExampleResource
        {
            Id = 1,
            Attr1 = "some",
            Attr2 = "more",
            Attr3 = "other",
            Attr4 = false,
            Attr5 = 123,
            Attr6 = default,
            Attr7 = default,
            Attr8 = default,
            Attr9 = DayOfWeek.Sunday
        };

        changeTracker.SetInitiallyStoredAttributeValues(resource);

        resource = new ExampleResource
        {
            Id = 1,
            Attr1 = "new",
            Attr2 = "change",
            Attr3 = "this",
            Attr4 = true,
            Attr5 = 456,
            Attr6 = default,
            Attr7 = default,
            Attr8 = default,
            Attr9 = DayOfWeek.Saturday
        };

        changeTracker.SetFinallyStoredAttributeValues(resource);

        changeTracker.HasImplicitChanges();
    }

    private sealed class ExampleResource : Identifiable<long>
    {
        [Attr]
        public string? Attr1 { get; set; }

        [Attr]
        public string? Attr2 { get; set; }

        [Attr]
        public string? Attr3 { get; set; }

        [Attr]
        public bool Attr4 { get; set; }

        [Attr]
        public int Attr5 { get; set; }

        [Attr]
        public DateTime Attr6 { get; set; }

        [Attr]
        public DateTimeOffset Attr7 { get; set; }

        [Attr]
        public TimeSpan Attr8 { get; set; }

        [Attr]
        public DayOfWeek Attr9 { get; set; }
    }
}

src/JsonApiDotNetCore/Resources/ResourceChangeTracker.cs

@@ -1,4 +1,3 @@
-using System.Text.Json;
 using JetBrains.Annotations;
 using JsonApiDotNetCore.Middleware;
 using JsonApiDotNetCore.Resources.Annotations;
@@ -13,9 +12,9 @@ public sealed class ResourceChangeTracker<TResource> : IResourceChangeTracker<TR
     private readonly IJsonApiRequest _request;
     private readonly ITargetedFields _targetedFields;
 
-    private IDictionary<string, string>? _initiallyStoredAttributeValues;
-    private IDictionary<string, string>? _requestAttributeValues;
-    private IDictionary<string, string>? _finallyStoredAttributeValues;
+    private IDictionary<string, object?>? _initiallyStoredAttributeValues;
+    private IDictionary<string, object?>? _requestAttributeValues;
+    private IDictionary<string, object?>? _finallyStoredAttributeValues;
 
     public ResourceChangeTracker(IJsonApiRequest request, ITargetedFields targetedFields)
     {
@@ -50,15 +49,14 @@ public void SetFinallyStoredAttributeValues(TResource resource)
         _finallyStoredAttributeValues = CreateAttributeDictionary(resource, _request.PrimaryResourceType!.Attributes);
     }
 
-    private IDictionary<string, string> CreateAttributeDictionary(TResource resource, IEnumerable<AttrAttribute> attributes)
+    private IDictionary<string, object?> CreateAttributeDictionary(TResource resource, IEnumerable<AttrAttribute> attributes)
     {
-        var result = new Dictionary<string, string>();
+        var result = new Dictionary<string, object?>();
 
         foreach (AttrAttribute attribute in attributes)
         {
             object? value = attribute.GetValue(resource);
-            string json = JsonSerializer.Serialize(value);
-            result.Add(attribute.PublicName, json);
+            result.Add(attribute.PublicName, value);
         }
 
         return result;
@@ -71,21 +69,21 @@ public bool HasImplicitChanges()
         {
             foreach (string key in _initiallyStoredAttributeValues.Keys)
             {
-                if (_requestAttributeValues.TryGetValue(key, out string? requestValue))
+                if (_requestAttributeValues.TryGetValue(key, out object? requestValue))
                 {
-                    string actualValue = _finallyStoredAttributeValues[key];
+                    object? actualValue = _finallyStoredAttributeValues[key];
 
-                    if (requestValue != actualValue)
+                    if (!Equals(requestValue, actualValue))
                     {
                         return true;
                     }
                 }
                 else
                 {
-                    string initiallyStoredValue = _initiallyStoredAttributeValues[key];
-                    string finallyStoredValue = _finallyStoredAttributeValues[key];
+                    object? initiallyStoredValue = _initiallyStoredAttributeValues[key];
+                    object? finallyStoredValue = _finallyStoredAttributeValues[key];
 
-                    if (initiallyStoredValue != finallyStoredValue)
+                    if (!Equals(initiallyStoredValue, finallyStoredValue))
                     {
                         return true;
                     }