feat: Add ECDSA signature vulnerability data

[oritwoen]

Summary

Extend boha to include ECDSA signature data for cryptographic research and vulnerability analysis.

Context

The btcsec ecosystem currently covers:

• Key generation vulnerabilities (vuke)
• ECDLP solving (kangaroo)
• Hash databases (shaha)

Missing: Signature vulnerability data - known cases of weak ECDSA signatures that can be used for:

1. Research and education
2. Testing signature analysis tools
3. Historical vulnerability documentation

Proposed Data Structure

pub struct VulnerableSignature {
    pub tx_id: String,
    pub address: String,
    pub r: [u8; 32],
    pub s: [u8; 32],
    pub z: [u8; 32],  // message hash
    pub vulnerability_type: VulnerabilityType,
}

pub enum VulnerabilityType {
    NonceReuse,
    BiasedNonce,
    LcgNonce,
    // ... future types
}

Data Sources

• Known nonce reuse transactions from blockchain
• Historical vulnerability cases (Android SecureRandom 2013, etc.)
• CTF/puzzle signatures

Provider Pattern

Following existing boha patterns: boha:signatures:nonce-reuse