Investigate Json overflow mechanism via Toth.Json

[kMutagene]

See https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/handle-overflow on System.Text.Json

In short, this can be used as a preliminary implementation to unblock #365 from #384/#385 . Untyped fields could target a specific field that is present on all datamodel types to dump the tokenized json there. After #385 is implemented, it is still useful work because the Dynamic object would just replace that field, but access to the tokenized json is still necessary to implement that.

[kMutagene]

@HLWeil could you shortly summarize your progress on this here so we can close this and focus efforts on #384 ? IIRC you solved this in a private repo