`Crypto`: Should `Key` be serializable?

[marcus-pousette]

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Currently you can not do

@field({type: Key}) 
key: PublicSignKey | PublicKeyEncryptionKey

only

@field({type: PublicSignKey}) 
key: PublicSignKey

[marcus-pousette]

Pros:

• Above example can be done

Cons:

• The serialized key will be more complicated, i.e. an additional discriminator and more deserialization paths (performance?)
• Composition patterns are better than inheritance. You can create your own crypto wrappers for serializing