feat: migrate to zerokit v2.0.1

[darshankabariya]

Bumps zerokit v0.9 → v2.0.1. Migrates the FFI from v0.9's raw byte buffers to v2.0's safer-ffi typed handles. Built against the stateless feature — the Merkle tree lives on-chain, so we no longer carry zerokit's pmtree-ft local tree.

What changed

• rln_interface.nim rewritten against the v2.0.1 typed-handle API (CFr, Vec_CFr, CResult*)
• Proof gen/verify wired through generateRlnProofWithWitness / verifyRlnProof
• verify_with_roots replaces verify_rln_proof — matches the contract's recentRoots ring buffer
• Wire format: 290-byte versioned encoding (layout in the rln_interface.nim header)
• Dead v0.9 buffer-API code removed

Checklist

• make librln builds against vendor/zerokit at v2.0.1
• Nim type-checks and links against the new librln
• Unit tests pass (make test)
• Roundtrip: membershipKeyGen → register → generateRlnProofWithWitness → verifyRlnProof
• Daily simulator E2E CI until RLN is enabled in logos.dev ( ci: add daily rln simulator e2e workflow #3885 )

After merged

• 48h soak on Logos fleet — no regressions in non-RLN paths
• Mix protocol functionality tested on Logos fleet (also uses zerokit 2.0.1)

Related issue

• feat: migrate to zerokit v2.0.1 #3868

[github-actions]

You can find the image built from this PR at

quay.io/wakuorg/nwaku-pr:3868

Built from 5ff5300