Reduce amount of target frameworks and add .NET 9 to test matrix

[Romfos]

Changes:

• Reduce amount of target frameworks: .NET 8 + .NET Standard 2.0
• Remove Microsoft.SourceLink.GitHub nuget. This is included in .NET 8 sdk, no need to use this package
• Added .NET 9 to test matrix

Motivation:

• .NET 6 EOL November 12, 2024 (https://devblogs.microsoft.com/dotnet/dotnet-6-end-of-support/)
• .NET 7 EOL May 14, 2024 (https://devblogs.microsoft.com/dotnet/dotnet-7-end-of-support/)
• .NET Standard 2.0 could be installable in .NET Framework 4.6.2+ and legacy .NET Core projects. No need to have separate tfm for older frameworks.
• Nuget package will have less size and restore is faster
• More easy for support

[Romfos]

please, help with review @JoshClose

[JoshClose]

I've seen some weird issues with nuget choosing the wrong framework and other odd stuff. That is why I have been building every version

[Romfos]

I've seen some weird issues with nuget choosing the wrong framework and other odd stuff. That is why I have been building every version

Maybe you have some example?
If we will have only .NET Standard version for older frameworks - you actually will have single version without variations

[Rob-Hague]

Related to #2324 (comment)?

[Rob-Hague]

BTW net462 is not fully compatible with netstandard2.0 (despite some documentation). I would recommend keeping a net462 target.

For example, if you put this in a netstandard2.0 library:

    public class Class1
    {
        public static string Go()
        {
            ECDsa ecdsa = ECDsa.Create(ECCurve.NamedCurves.brainpoolP256r1);

            return Convert.ToBase64String(ecdsa.ExportParameters(true).D);
        }
    }

and call it from a net462 app:

using ClassLibrary1;

Console.WriteLine(Class1.Go());

Console.ReadLine();

It will build but get a runtime error. (System.TypeLoadException: 'Could not load type 'NamedCurves' from assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.')

[Romfos]

@Rob-Hague as far as I know - CsvHelper doesn't use any API that is not compatible with NET FX. I think that compatibility is not an issue for this library. Or am i wrong?

List of test platforms in tests: net9.0;net8.0;net48;net47;net462

#2324 (comment)
System.Runtime.CompilerServices.Unsafe update fix this issue

[JoshClose]

I'm going to continue to publish a build for each available framework. I read up on this a little and the compiler can use optimizations for each framework and other things.