Update TimeOnly ToXmlString to include time zone offset

- Change ToXmlString(TimeOnly) to output "HH:mm:sszzz" with local offset
- Update unit test to match new format with time zone info
- Bump Verify.Xunit package to v31.12.5

Author: Gregory Nikolaishvili

Directory.Packages.props

@@ -14,7 +14,7 @@
 
 	<PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.*" />
 	<PackageVersion Include="Verify.SourceGenerators" Version="2.5.*" />
-	<PackageVersion Include="Verify.Xunit" Version="31.9.3" />
+	<PackageVersion Include="Verify.Xunit" Version="31.12.5" />
 	<PackageVersion Include="xunit" Version="2.9.3" />
 	<PackageVersion Include="xunit.runner.visualstudio" Version="3.1.5" />
 	<PackageVersion Include="coverlet.collector" Version="6.0.4" />

src/AltaSoft.DomainPrimitives/ToXmlStringExt.cs

@@ -35,8 +35,17 @@ public static class ToXmlStringExt
     /// </summary>
     /// <param name="value">The TimeOnly value to convert.</param>
     /// <returns>The XML string representation of the TimeOnly value.</returns>
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static string ToXmlString(this TimeOnly value) => value.ToString("HH:mm:ss", CultureInfo.InvariantCulture);
+    public static string ToXmlString(this TimeOnly value)
+    {
+        var date = DateOnly.FromDateTime(DateTime.Today);
+
+        var localDateTime = date.ToDateTime(value, DateTimeKind.Local);
+        var dto = new DateTimeOffset(localDateTime);
+
+        return dto.ToString("HH:mm:sszzz", CultureInfo.InvariantCulture);
+    }
 
     /// <summary>
     /// Converts a <see cref="DateTimeOffset" /> value to its XML string representation

tests/AltaSoft.DomainPrimitives.XmlDataTypes.Tests/ToXmlStringExtTests.cs

@@ -24,7 +24,7 @@ public void TimeOnly_ToXmlString_ReturnsExpectedFormat()
     {
         var t = new TimeOnly(13, 45, 30);
         var xml = t.ToXmlString();
-        Assert.Equal("13:45:30", xml);
+        Assert.Matches(@"^13:45:30(?:Z|[+-]\d{2}:\d{2})$", xml);
     }
 
     [Fact]