Function parse 

pub fn parse(spec: &Value, argv: &[String]) -> Result<Value, String>

Parse argv against spec. Returns a CliParsed-shaped JSON value on success, an error message on failure.

CliParsed shape:

{
  "command":     ["rubric", "scan"],   // path of subcommand names
  "flags":       { "verbose": true },
  "options":     { "output": "report.json" },
  "positionals": { "path": "./src" },
  "remaining":   []                    // args after `--` separator
}