Add Rust binding: openttt-rs crate

[Heime-Jorgen]

Summary

OpenTTT is used in Ethereum execution-specs tooling and blockchain validation pipelines — environments where Rust is the dominant language. A openttt-rs crate would enable native integration without Node.js dependency.

Scope

• Implement generate_pot() + verify_pot_signature() in Rust
• Publish as openttt-rs on crates.io
• Ed25519 signing: use ed25519-dalek or ring
• Multi-source time fusion (NIST/Cloudflare/Google NTP) via async HTTP or NTP

Acceptance Criteria

• cargo add openttt-rs works
• PotSigner::new() generates Ed25519 keypair
• generate_pot(agent_id, sources) returns a PoTToken struct
• verify_pot_signature(pot_hash, signature, public_key) returns bool
• cargo test passes

References

• TS reference implementation: src/pot_signer.ts
• PoT wire format: YELLOW_PAPER.md

Difficulty

Medium — pure Rust, no blockchain knowledge needed. Requires async HTTP for NTP fetching.