Ed25519LittleEndianEncoding is not serializable

[MatthewPhinney]

I wrote an AttributeConverter to map an EdDSAPublicKey to/from bytes, but when testing it, I found

org.springframework.orm.jpa.JpaSystemException: could not serialize; nested exception is org.hibernate.type.SerializationException: could not serialize
Caused by: java.io.NotSerializableException: net.i2p.crypto.eddsa.math.ed25519.Ed25519LittleEndianEncoding

This can easily be fixed by making Encoding serializable. Ed25519ScalarOps must also be serializable for the Hibernate converter to work, and it may be sensible to have BigIntegerScalarOps serializable as well.