Harden BLS12-381 Groth16 and PlonK for testnet readiness

[satran004]

Summary

This PR implements the BLS12-381 Groth16 and PlonK public-testnet readiness work from ADR-0022 through ADR-0025.

It hardens the supported Cardano BLS12-381 paths end to end across prover setup, importers/codecs, off-chain verifiers, on-chain Julc validators, documentation, and release gates. BN254 is moved behind explicit legacy opt-in because Cardano currently exposes only BLS12-381 builtins.

Key Changes

Groth16 hardening

• Adds stricter BLS12-381 Groth16 public-input range checks.
• Rejects non-canonical, infinity, off-curve, and off-subgroup proof/VK points.
• Hardens both pure Java and native/blst verifier paths.
• Hardens Groth16BLS12381Lib for on-chain scalar and point validation.
• Adds Groth16 on-chain negative tests, including malformed and infinity points.
• Disables accidental BN254 use through explicit legacy opt-in policy.

PlonK hardening

• Hardens BLS12-381 PlonK prover/setup and verifier paths.
• Adds independent snarkjs BLS12-381 PlonK verifier test vectors.
• Adds Cardano-profile PlonK proof/VK conversion for on-chain use.
• Adds bounded multi-public-input PlonK verifier profiles.
• Adds script-parameter and datum-input PlonK MPI validator variants.
• Moves the transcript prototype out of deployable main sources.
• Adds PlonkBLS12381Lib as a reusable Julc @OnchainLibrary.
• Refactors built-in PlonK validators to delegate to the reusable library.
• Adds guard tests so non-verifying PlonK prototypes cannot be deployed.

Trusted setup and cache

• Requires explicit insecure setup opt-in for development Powers of Tau / SRS generation.
• Splits Groth16 and PlonK setup cache APIs for clarity.
• Adds versioned, hash-bound setup/SRS cache payloads.
• Revalidates cached BLS12-381 points on load.
• Stops persisting tauScalar in default cache files.
• Adds explicitly named insecure dev-only tau persistence API.

Codec and importer hardening

• Adds bounded reads and typed failures for untrusted inputs.
• Hardens R1CS, zkey, ptau, witness, JSON, and CBOR decoding paths.
• Adds canonical field parsing and duplicate-key rejection.
• Adds zkey hash pinning and BLS12-381 point validation where applicable.

Documentation and ADRs

• Adds ADRs 0022, 0023, 0024, and 0025.
• Adds PlonK hardening review/response and production-readiness notes.
• Adds beginner trusted-setup/SRS guide.
• Updates user docs to distinguish public-testnet readiness from value-bearing/mainnet readiness.
• Documents that reusable on-chain verifier libraries verify only the cryptographic proof statement; application validators must enforce replay/nullifier/
  authorization policy.

Validation

Downstream validation was also performed in zeroj-usecases using the locally published artifact:

• Proof-of-reserves PlonK local tests
• Compliance-credential PlonK local tests
• Proof-of-reserves PlonK Yaci DevKit E2E
• Compliance-credential PlonK Yaci DevKit E2E