feat: add mathematical proof tests for OPRF security properties

- Add test_proof_of_fingerprint_linkability proving split-blinding is broken
- Add test_proof_of_linkability proving deterministic r,e is linkable
- Add test_proof_of_noise_instability proving fresh random breaks correctness
- Add test_proof_of_fingerprint_in_proposed_fix proving r_pk fix is unlinkable
- Refactor ntru_lwr_oprf.rs for clarity
- Add anyhow dependency for error handling

Cargo.toml

@@ -33,6 +33,7 @@ thiserror = "2"
 zeroize = { version = "1", features = ["derive"] }
 
 subtle = "2.5"
+anyhow = "1.0.100"
 
 [dev-dependencies]
 tokio = { version = "1", features = ["full", "test-util"] }