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
