Update dependencies and adapt library version to newer target-frameworks

[Sella-GH]

Description

The current target framework (TFM) for .NET 5 is outdated and EoL since 2022-05-10. The library is compatible to newer versions but it should be adapted to the newer TFMs for better compatibility and usage of newer features which improve the code quality.

Proposal

Use a newer TFM maybe even at least .NET 6 (which is outdated since 2024-11-12 but Microsoft now recommends to use nothing less than at least .NET 6 for projects now) with an optional TFM to .NET 8 too. Since .NET Standard 2.0 is compatible to both of them there would be no issue.

Use a newer version of C# shipped with the TFMs and align the code to it so you can use newer features.

Update all your current used packages since the library currently ship packages with Deprecation status and Security Issues:

• Microsoft.Extensions.Http.Polly
• System.Text.Json

Also some of the other packages could also use some updates as there are transitive packages with Security Issues:

• Newtonsoft.Json
• System.Net.Http
• System.Text.RegularExpressions