Enhancement: serializer control tokens

[gitmodimo]

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I need to control precision of json serializer for specific fields. It would be perfect to for example push something like setPrecisiin token before and after field value.

I think it could be implemented with FieldParams optional field that could be set by user implementwtion upon field visit. It could be in a form of some kind control token factory invoked before and after token value visit. The token itself could work just like reserve token.