Custom Attributes in .NET: retarget to net10.0, add the reading-API examples

[vladimir-pecanac-main]

Updates the sample for the article "Custom Attributes in .NET" (https://code-maze.com/dotnet-custom-attributes/).

Only aspnetcore-features/CustomAttributes changes.

• Both projects move from net6.0 to net10.0.
• Test packages, re-queried on NuGet 2026-10-11 (latest stable): Microsoft.NET.Test.Sdk 18.10.1, MSTest.TestAdapter 4.5.1, MSTest.TestFramework 4.5.1, coverlet.collector 10.1.0. The project keeps the MSTest.TestAdapter + MSTest.TestFramework pair it already used.
• GetAttribute: the "atributes" typo in the not-found message is fixed.
• GetAttributesOfMethods: Type.GetMethods returns an empty array, never null, so the guard checks Length only.
• The unused Visual Studio using headers are gone, every file uses a file-scoped namespace, and the list is declared with var.
• New in CustomAttributeHelper: GetAttributeGeneric (the GetCustomAttribute extension method), HasAttribute (IsDefined) and CountInheritedAttributes, which reads an inherited attribute through Attribute.GetCustomAttributes and through MemberInfo.GetCustomAttributes.
• TaskBoard and TeamTaskBoard carry an inherited [Reviewed] attribute on a virtual property and a virtual method. The test shows the static method finds it on both, while the instance method ignores inherit on the property only.
• Three new tests cover the new helpers. No test name contains Live.

Local run on SDK 10.0.302, runtime 10.0.10: build 0 warnings 0 errors, dotnet test Passed 6 Failed 0, dotnet list package --vulnerable --include-transitive clean on both projects. Program.cs is unchanged.