[Deliverable] Integrate and benchmark Poseidon2 hash function

[jm-clius]

Owner: AnonComms Zerokit

FURPS:

• F2. Zerokit supports Poseidon2 as an alternative hash function alongside Poseidon
• F3. Zerokit supports the automatic generation of round parameters for both Poseidon and Poseidon2
• U6. The hash function selection (Poseidon vs Poseidon2) is exposed via the runtime configuration enum
• U7. The implementation of the new Poseidon2 circuit has been completed and documented in the circom-rln repo
• R1. Poseidon2 proofs verify correctly and Poseidon behavior remains unchanged when Poseidon2 is enabled
• P1. Poseidon2 proof generation is benchmarked against Poseidon and demonstrates measurable improvement
• S3. New Poseidon2-related functionality and APIs are fully exposed through the FFI and WASM interfaces

Checklist:

• Code: link to GitHub issues/PRs/Epic
• Dogfood: link to dogfooding session/artefact
• Docs: links to README.md or other docs