Harden gen_inputs.sh: validate inputs and fail on malformed witness data

[Psalmuel01]

Summary

circuits/scripts/gen_inputs.sh builds Prover.toml inputs but does minimal validation. Malformed values produce cryptic nargo/bb failures downstream. Add input validation and clear errors.

What to build

• Validate each expected field is present and well-formed (numeric where numeric, 0x-hex where field, correct byte lengths for keys/sigs)
• Fail fast with a message naming the offending field
• set -euo pipefail and quoting audit

Acceptance criteria

• Missing/malformed inputs produce a clear, field-named error before nargo runs
• Script is shellcheck-clean
• Existing build flow (build.sh) still works end-to-end---

✅ Merge requirements (read before starting)

Before this PR can be merged, all of the following must hold:

• All CI checks pass (contracts, frontend, circuits as applicable)
• Every Greptile review comment is addressed — no unresolved review threads
• Greptile confidence score is 4/5 or higher

Greptile performs the detailed code review on each PR. Please resolve its feedback fully before requesting a human merge — PRs below 4/5 or with open Greptile threads will not be merged.

[drips-wave]

Congratulations, @AbdulCoderr! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @AbdulCoderr: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

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[Psalmuel01]

@AbdulCoderr kindly resolve the conversations, your greptile score is 1/5. it was stated in merge requirements it has be at least 4/5