XML Serialization in C#: retarget to .NET 10 and run the examples from Program.cs

[vladimir-pecanac-main]

Updates the sample for the article "C# XML Serialization: Serialize Objects With XmlSerializer" (https://code-maze.com/csharp-xml-serialization/).

Changes, all inside xml-csharp/XMLSerializationInCsharp:

• Both projects move from net5.0 to net10.0.
• Program.cs printed "hello world". It now uses top-level statements to serialize one Patient twice and print both documents: once with a StreamWriter (the article's first example) and once with an XmlWriter using XmlWriterSettings (indentation, UTF-8 without a byte order mark) and an empty XmlSerializerNamespaces, so the root element has no xmlns:xsi or xmlns:xsd (the article's new last section).
• New test XMLSerializationUnitTest_v6 checks that second example: no byte order mark, no namespace declarations, and the expected document with an encoding="utf-8" declaration.
• The five existing test classes are unchanged. Their Assert.AreEqual calls compile and pass on NUnit 5.0.0.

Package versions, looked up on NuGet on 2026-10-10 (latest stable):

• Microsoft.NET.Test.Sdk 18.10.1 (was 16.9.4)
• NUnit 5.0.0 (was 3.13.1)
• NUnit3TestAdapter 6.3.1 (was 3.17.0)
• coverlet.collector 10.1.0 (was 3.0.2)

Local results on SDK 10.0.302 / runtime 10.0.10: dotnet build -c Release 0 warnings, 0 errors; dotnet test 7 passed, 0 failed; dotnet list package --vulnerable --include-transitive reports no vulnerable packages in either project.