Fix incorrect RSA identity key fingerprint generation

The fingerprint calculation was using PKIX encoding instead of the
required PKCS1 DER encoding for RSA public keys. This affected both
the relay identity resource and obfs4 node ID derivation.

- Use x509.MarshalPKCS1PublicKey instead of x509.MarshalPKIXPublicKey
- Add test case with known fingerprint vector to prevent regression
- Update both generateFingerprints and deriveNodeIdFromRsaKey functions

fixes #2

internal/provider/tor_obfs4_state_resource.go

@@ -406,11 +406,7 @@ func (r *TorObfs4StateResource) deriveNodeIdFromRsaKey(rsaPrivateKeyPem string)
 		return nil, fmt.Errorf("failed to parse RSA private key: %w", err)
 	}
 
-	// Extract the public key and encode it
-	publicKeyBytes, err := x509.MarshalPKIXPublicKey(&privateKey.PublicKey)
-	if err != nil {
-		return nil, fmt.Errorf("failed to marshal public key: %w", err)
-	}
+	publicKeyBytes := x509.MarshalPKCS1PublicKey(&privateKey.PublicKey)
 
 	// Generate SHA1 hash of public key (this is the relay fingerprint/node ID)
 	hash := sha1.Sum(publicKeyBytes)