Type system for FKL

[phodal]

Is your feature request related to a problem? Please describe.

For example: YANG Data model: https://www.rfc-editor.org/rfc/rfc6020

typedef percent {
     type uint8 {
         range "0 .. 100";
     }
     description "Percentage";
 }

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Describe alternatives you've considered
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Additional context
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