In .NET 9, remove dependency on Microsoft.Extensions.Primitives by using Span<char> instead of StringSegment

[WalkerCodeRanger]

The version parsing uses Microsoft.Extensions.Primitives.StringSegment to efficiently pass subsegments of strings without constructing new string instances. That library supports all the versions that the semver library does and provides all the needed functionality. As of .NET 9, Microsoft is adding additional methods to do things like split a Span<char> at separator characters. With that, there should be enough support in the BCL to implement semver in terms of Span<char> instead. That would eliminate the dependency on Microsoft.Extensions.Primitives, thereby reducing installed size in apps using the library and avoiding any conflicting dependency version issues.

I will investigate doing this for the next patch version. However, if it causes too much mess in the code to support a variation for newer versions, I may not do this.