Low level sdk helper

[Jumongweb]

Summary

closes #56

Add a low-level SDK helper for building a ready-to-sign Soroban verification transaction from a raw snarkjs Groth16 proof.

What changed

• implemented buildVerifyCall(proof, publicInputs, contractId, networkPassphrase) in sdk/src/verify.ts
• accept raw Groth16 proofs in snarkjs shape (pi_a, pi_b, pi_c) and encode them into Soroban-compatible proof bytes internally
• encode public inputs from hex strings into Soroban Vec arguments
• surface malformed proof/input failures as typed ProofEncodingError
• added fixture-backed unit coverage for:
  • successful transaction construction from a known pre-generated proof
  • correct proof byte packing into the contract call
  • both testnet and mainnet passphrases
  • malformed proof rejection

Verification

• cd sdk && npm test -- --run src/verify.test.ts
• cd sdk && npm run typecheck

[leocagli]

Hi @Jumongweb 👋 — two things before this can be reviewed/merged:

1. Required check failing: Frontend fails (Contracts/SDK/SDK bindings/Circuit artifacts are green).
2. Missing evidence: please add a video or screenshots showing the SDK helper working.

Happy to merge once both are green. 🙏

[leocagli]

Hi @Jumongweb 👋 — quick update: video/screenshots are not required to merge anymore, just a bonus — if you add one it'll be considered for GrantFox rewards on this issue. So I'll review this on code + checks alone now. 🙏