feat: implement verification and claim with Poseidon hash

[wheval]

Closes #112

• Replaced hardcoded verification codes with Poseidon-based secure generation
• Added generate_claim_code() function for Poseidon-based claim code generation
• Updated create_claim() to automatically generate secure codes instead of accepting user input
• Removed claim_code parameter from create_claim() interface for cleaner API
• Added VerificationData and ClaimData structs for structured Poseidon hashing
• Updated all verification and claim tests to work with generated Poseidon codes
• Added 3 new tests specifically for Poseidon claim code functionality
• Ensured consistent Poseidon usage across all verification/recovery/claim systems

[GoSTEAN]

LGTM