Add more zero-knowledge proof examples

[tob-joe]

Overview

Add additional zero-knowledge proof examples to demonstrate the Decree library's capabilities and provide reference implementations for common cryptographic protocols.

Existing Examples

• Girault proof (test in tests/inscribe_tests.rs)
• Schnorr proof (test in tests/inscribe_tests.rs)

Possible Options

Simple Examples (Sigma Protocols)

• Chaum-Pedersen proof - equality of discrete logarithms (Add Chaum-Pedersen proof example #10)
• Product proof - prove z = x * y given commitments
• Range proof - prove 0 ≤ x < 2^n using bit-by-bit approach

Complex Examples (Beyond Sigma Protocols)

• Small-factor proof - prove RSA modulus has factors above threshold (Add small-factor proof from CGGMP21 #14)
• Paillier-Blum modulus proof - prove N = pq with p ≡ q ≡ 3 (mod 4) (Add small-factor proof from CGGMP21 #14)
• MPC-in-the-head proof (e.g., Ligero-style) - demonstrates complex multi-round Fiat-Shamir
• Inner product argument (Bulletproofs-style) - shows recursive proof structure

Implementation Guidelines

• Use Ristretto255 for elliptic curve examples
• Include comprehensive test suites in example files
• Focus on clean implementations
• Demonstrate proper use of the Inscribe trait with domain separation