fix: validate what goes inside criteria, not just the container

[simonx1]

The builders were inconsistent about the same job. choice and score checked the type and size of their criteria; noul took whatever it was given and shipped it.

Questions.noul("Urgent?", criteria: ["yes", "no"])
# => {"type"=>"noul", "instructions"=>"Urgent?", "criteria"=>["yes", "no"]}  -> 422 from the API
Questions.noul("Urgent?", criteria: { "yes" => "means urgent" })
# => also built happily; the documented keys are true/false

None of the three looked at descriptions, so a score level or an option rubric could be an Integer and go over the wire as one.

Choice labels had a quieter problem. They're stringified to become JSON keys, so { billing: "...", "billing" => "..." } collapsed into one option carrying whichever description came last. The question that reached the model was not the question that was written, and nothing said so.

The fix

• noul criteria must be a Hash keyed by true/false (the booleans read best at a call site and are stringified for the wire, which is what JSON would have done anyway). One-sided criteria are fine.
• Descriptions in all three builders are an EntryType: String, Hash, Array, or nil for undescribed.
• Colliding and blank choice labels raise.

The 255-option and 2..10-level caps already matched the docs and are unchanged.

Tests

14 new cases in test/questions_test.rb.

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Draft: part of a security and API-coverage audit, opened for reference rather than as a request for immediate review. Independent of the other branches, each off main. Suite green on Ruby 3.2.11, 3.3.8 and 3.4.8.

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