Remove explicit STJ dependency for net 8

[thompson-tomo]

Is your feature request related to a problem? Please describe.
I want to minimise dependencies in my project by utilising framework dependencies wherever possible

Describe the solution you'd like
I want the package to not have an explicit dependency on System.Text.Json as it can be provided by the framework.

Describe alternatives you've considered
Accept the additional dependency

Additional context
n/a

[Numpsy]

On a semi-related note, the version 8.0.0 System.Text.Json NuGet package that is currently being referenced is listed as suffering from GHSA-hh2w-p6rv-4g7w, and using the inbox version of System.Text.Json where possible might help to minimize that sort of issue.

[thompson-tomo]

@Numpsy Totally agree by leveraging framework dependencies where ever possible we can reduce effort on package maintainers while helping to make less vulnerable dotnet eco-system.