[Feature] - Support older LTSC runtimes

[smaillet]

Is your feature request related to a problem? Please describe.
I Can't use this library with apps targeting older runtimes. (Roslyn Source Generators/Analyzers require .NET standard 2.0)

Describe the solution you'd like
Support consumers that target older versions of the .NET runtime

Describe alternatives you've considered
Essentially clone the code internally. Ugh...

Additional context
This is a common problem. That any library needs to look at and understand. If not using runtime specific support (like static abstract) then it is at least plausible to use the library in .NET standard 2.0. It can, and IMNSHO, should, set the LangVersion property in the project. (Sadly, VS FORCES a locked step with the runtime, but it can be overridden by modifying the project file itself)

[smaillet]

SemVer type uses multiple interfaces with "static abstract" so .NET standard 2.0 support is difficult at best. (Requires significant preprocessor differences AND all of the tests ported to validate correct behavior in either case... So, unless there is a VERY compelling reason to support back to .NET standard 2.0 that's not really of interest here. Supporting the LTSC of .NET 8.0 is reasonable though.